Worst experience with customer service

I tried home internet for a few months and due to signal strength issues I canceled.  They gave me a prepaid label to send the modem back via UPS which I did on 1/27/23.  A couple months later I get a bill for $400 because they claim I didn't send it back.  I called and I gave them the tracking number which shows it was never even used.  She openly admitted that they were having some issues with tracking numbers and I asked her to look up the IMEI which led to her stating that it appeared to be in their possession.  

They opened a Handset Order Research ticket (?) and said this will get resolved.  I've called at least 7 times and received 3 more bills saying I still owe.  On the last call they said on April 9th the Handset Order Research "team" is processing this and the bill will show a zero balance on May 9th and "not to worry, this will be taken care of".  So instead of removing it from my bill, they sent me to collections.  I'm absolutely infuriated with T-Mobile.  If they would NOT have kept telling me not to worry and this will be removed but told me I was going to be sent to collections, I would have just paid the dang thing.  

So I called back and told them instead of removing my bill, i'm not being contacted by collections.  They literally told me they're going to open a Handset Order Research ticket.  It's like starting over every time.  So, I called collection agency and just paid it.  So now my balance is $0.  But again, I get another email this morning stating there is an update to my Handset Order Research ticket and to call.  So I sit on hold and the girl pulls up my info and says they don't even know why that was sent and will call me tomorrow (which they never call back).  I've heard this 7 times now.  Just a complete joke.  

So thank you T-Mobile.  I'm happy you stole $400 from me for a modem I returned and they openly admitted to having the modem in their possession.  I have all of these calls recorded and it's really sad to be tossed around like this.  It's pretty bad when you make Comcast support look excellent.  The only good thing about this whole mess is I now know to never use T-Mobile for anything ever again.  Worst experience ever and now I'm out $400 for a modem I returned.  Gracias.