T-MOBILE LOST MY TRADE IN

I pre-ordered the 14 pro and received it in September, so I shipped back my old phone to receive the credit for it. Tracking shows it was delivered on the 28th of September, but I kept getting texts that I needed to ship my phone in, and that was weird, considering they had already gotten it, right? So I contacted customer support not once but TWICE in October, and both reps assured me that my phone was received and that I'd receive my credit on next months bill (November). I got my bill for November, and the old phone is STILL on there...so again, I contacted customer support, and they said they'd escalate it and figure out what was going on. Today (November 11th) I received an email saying they couldn't locate my phone in their warehouse…. I am highly considering changing carriers because this is absolutely unprofessional. How does a company this large manage to lose people's phones constantly?? And no, I don't have the issue resolved yet, so if anyone has advice, please send it my way.