Feeling misguided

In November of 2024, I placed a call about upgrading my iPhone 15 for a iPhone 16 pro.  I was told that I could not at that time by a representative.  I was called back from another representative who told be they were looking in to being able to trade my iPhone 15 for the iPhone 16 pro.  He told me he would reach out to me in a week, but never did.  I made a call to customer care on December 09,2024 and  asked about the rep who called speaking about my trade in.  The young lady put me on hold.  Once she came back she said that I would be able to trade in the iPhone 15 for the 16 pro.  I asked did I have to do it with T-Mobile for could I go to the apple store. Her reply was either one would do.  I went to the apple store and completed the transaction. A long story short, I noticed the iPhone 15 was still on my account and I was still be charged for it.  I've been dealing with different representative since then and they are saying I was not eligible to do that. I said that they need to listen to their calls from that day I spoke with her and the prior guy who called me to say they were looking into the situation because they think that transaction could happen.  There was a ticket created on 1-12-24 about this situation.  I was told they will listen to all of the calls to prove what I was told and also hold that representative accountable.  Well in March I was told they would adjust my plan because they still had not checked the calls from December and they probably not available now.  Prior to that call I was constantly speaking to people from January until March with a lot of failed promises about reaching to that particular representative.  They even pretended not to see some of the call leading to this whole issue.  I had to tell them all of the calls with the dates, time stamp, and duration which I stated to them if I can see them so can they.  I was told they could not adjust or find a plan to be sufficient with my grandfathered plan.  I have been with T-Mobile for 18 years and have never experienced such poor service since it clearly happen from one of their representatives speaking bad information.  I am still stuck paying for a phone that I no longer have due to their negligence.  There does not seem to be a direct phone number to reach the Corporate office.  I am in need of help with this situation.  I do know they have all of the notes but no one wants to listen to that call, but I'm sure it had been my error they would have played the recording to me right away.  Thank you all for reading this post.