Promoción n.° 16 de "intercambio de Apple" de 2021

I did an Apple Trade-In offer in September 2021 turning in my iPhone X for which I was supposed to get $800. The terms were for 24 months, I am now at 29 of 24 (mind you) with 1 more month to go. I am getting $21.84 credit a month. So far I only have $633.36 credited and it will be $655 by the time I am done. THIS IS NOT the $800 promised (and no it wasn't up to $800). I actually have a screenshot of the offer. I am very disappointed and wished TMobile would stick with their original offer. Anybody else had this issue?