Trade in bill credits CANCELLED?

I'm having a similar issue.   On July 13, 2021 I spoke to a T-Mobile rep and verified that my Galaxy S8 was eligable for a $500 trade-in toward a Galaxy S21 5G.   On July 19, 2021 I went online, purchased the phone (actually 4 of them - all the lines in my plan) and on each one received two confirmation emails saying that upon receipt of my working phone I was to receive a $15 trade in plus 24 monthly bill credits of $20.21, the total of which is $500.00.   When I saw my bill, it showed credits of $7.83 on each line which when added to the $15 comes out to $200.   After several phone calls I finally spoke to someone willing to listen and was told that my promotion did not exist on July 19, 2021 even though that's what the website allowed me to do and the confirming emails verified.   She agreed to go back to the Promotions department and try to get my bills adjusted.   That was over 10 days ago.  I just heard back from them today saying that had not heard back from the promotions department.   I explained that if they didn't fix it to my satisfaction I would be asking for my old phones back and cancelling the contract and switching carriers but so far nothing has changed.  Has anyone else had a similar experience?   I have always been happy with T-Mobile, both cell service and customer service.  I really don't want to change but I will if this doesn't work out!