Trade in value of my iPhone misrepresented

If you read the terms and conditions of the trade-in promo.  It clearly states that you can receive up to whatever amount is the highest value for that mode.  Most devices never reach that amount though for a few reasons.  

We had the exact same situation with trade-in.  We were told that I would pay maybe $100 more for IPhone 15 Pro with trade-in of 13 Pro and that my husband would pay nothing for an  IPhone 15 with trade in of  IPhone 13.  Much to our surprise, we were allowed a very nominal trade-in and I was told that I would owe almost $700 for the phone and that he would owe close to $500. The bill reflects this.  I feel it was bait and switch.  This trade up every two years is not how it was represented to us in the sales spiel.  Very unhappy with the deception. 

Say they give you 1000 for the iPhone. It'll take the base 100 and take it our of bill, and the other $900 will be in bill credits over 24 mmonths. This has always been what happens when I take advantage of the promos. Also depending on which cycle you are on the promotion may take up to 2 billing cycles. 

You are right, that is how it SHOULD be, but that is not how it IS. 

How was yours setup? Has T-Mobile got your trade in and inspected it yet?  Got to give more information.