Be an advocate for yourself and tell the customer service rep you believe you're being scammed and that they do have your phone. I had the same issue except I was receiving the trade in credit for two months and then it went away. I did a lot of research and found people having similar issues so I called customer service and basically demanded that they adjust my bill to reflect the trade in credit and the representative ended up adjusting my bill. She also told me that they believe there was damage with my iPhone and someone was going to call me back within the next month to tell me what happened (side note: I had already heard from a store rep that the warehouse was saying they never received my trade in decide). Five hours later I got a call at 8:30pm with a representative from the warehouse investigation team saying my device was nowhere to be found and that they couldn't do anything. She proceeded to say the only solution was to file a claim with UPS. Luckily, I had already looked into filing a claim with UPS but UPS doesn't allow you to file a claim after 60 days (this is now 70+ days after my device was delivered). I responded to the customer service agent very sternly telling her the info about a UPS claim and that I'm now stuck in this position where nothing can be done. I continued on to say that I believed T-Mobile has my device and they're lying to me and scamming not only me but many other people. I told her I found this page and many other posts about people running into the same problem. The minute I mentioned scam she "conveniently" found my phone.
 

MY ADVICE: if you have proof from UPS of delivery and it's a couple months later, be an advocate for yourself. Tell them you believe you're being scammed and that they have your phone. I'd be curious to know how many people will all of a sudden get an answer that their phone has been found when they mention this information. 

I submitted an incident to https://www.t-mobile.com/responsibility/legal/integrity-line earlier today for my trade in phone that was "lost" in transit.  I labeled the incident as fraudulent behavior.

They have already contacted me trying to resolve the issue.

andreasav1 may be on to something.

This is been happening to too many for too long.

mross5150 wrote:

First time happing to us but same issue.  For the past couple of years we have bought and traded in our phone online. No hay problema.

This time we received the new phone.  I boxed up the trade in and correctly packaged and labeled it like I always have.  I tracked the box until it showed delivered to Dallas TX.  2 months later the trade in phone was never checked in at the warehouse.  After 5 phone calls to T-Mobile I was finally told I would have to file a claim with the USPS to recover my money from the trade in phone.  Meanwhile the charges for the traded in phone continue to appear on my bill.  I will never mail in a phone again.

I used their label, where there is a USPS tracking. The USPS tracking showed that it was delivered.

I contacted T-Mobile and they started a case for investigation. Within 10 days, the issue was solved, and they sent the credits to me

First time happing to us but same issue.  For the past couple of years we have bought and traded in our phone online. No hay problema.

This time we received the new phone.  I boxed up the trade in and correctly packaged and labeled it like I always have.  I tracked the box until it showed delivered to Dallas TX.  2 months later the trade in phone was never checked in at the warehouse.  After 5 phone calls to T-Mobile I was finally told I would have to file a claim with the USPS to recover my money from the trade in phone.  Meanwhile the charges for the traded in phone continue to appear on my bill.  I will never mail in a phone again.

T-Mobile sued after employee stole nude images from customer phone during trade-in, https://www.cnbc.com/2023/11/17/t-mobile-sued-after-employee-stole-nude-images-from-phone.html

Why not sue them again, if you have experiences in these trade-in lost or scams?

It's just happened to me same story 10-11-2023 package arrived but supposedly no device in this is Bs they blaming usps 

This sound like it's a Assurant scam or someone in warehouse stealing the Phones 📱  it just happened to me last month October 11-2023 they received package but said no phone returned this is Bs now they charging almost $700 for a defective phone stay away from T-mobile Assurant insurance not safe trust me

Please ensure that all communication documentation is retained by everyone involved. Our intention is to explore the possibility of engaging a lawyer for potential legal action as a class. We find the situation at hand highly unacceptable and regard it as an evident scam.

I am facing a similar issue with my phone trade-in. After bringing my phone to the store for inspection and verification, everything seemed fine until they discovered that the IMEI was incorrect. I was advised to contact customer service, which I did, and they provided me with a prepaid label via email. I securely packaged the phone along with a note explaining the incorrect IMEI and mailed it back using the provided prepaid label.

It has now been a month since the USPS tracking confirmed the delivery of the package. Upon contacting T-Mobile, I was informed that they do not see any record of the package being scanned into their system. Therefore, they suggest filing a claim with USPS. This situation is deeply frustrating and feels like a fraudulent act. T-Mobile utilized a third-party service called Assurance, and they appear to be confident in their belief that the item was either not received or that I sent an empty box. It is disheartening that the blame is being shifted onto the customer or USPS without taking responsibility for any potential human error on their part.

I request that T-Mobile thoroughly investigate this matter and ensure that appropriate actions are taken to rectify the situation. Your prompt attention to this issue would be greatly appreciated.

Please ensure that all communication documentation is retained by everyone involved. Our intention is to explore the possibility of engaging a lawyer for potential legal action as a class. We find the situation at hand highly unacceptable and regard it as an evident scam.