I got the iPhone X as part of the promotion Tmobile had when iPhone X came out. You would trade in an eligible phone (in my case an iPhone 6 plus) and would get a monthly bill credit of $12.50 over 24 months. I got confirmation they received the iPhone and were processing the discount. I noticed that the monthly bills would come and no discount. Called them every month and at the beginning the rep would say to give it another month to show on my bill. Last time i spoke with someone two months ago said that i would get a prorated discount for months i didn't get the discount in one bill and then following month would start seeing the $12.50 deduction. It still hasn't happened yet. NO discount. This same problem happened to someone else I know. I feel cheated and would never trade in my phone to Tmobile again.
Oh man! I know the iPhone X is an expensive device so a promise of a promotion is definitely a deciding factor on your purchase. We are going to need to take a closer look at your account to see what specifically is going on here. If you have a Facebook or Twitter account, I would recommend that you use the links in my signature to message our T-Force team. They will be able to look at you account in it's entirety and see what happened with this promotion.
Manage your T-Mobile account