Xfinity service gives me anxiety - not resolved after 12 months

TLDR, I traded in a iphone 12 which I received a confirmation of $700 credit for in Oct-23. That $700 should have been applied over the course of 24months, i.e ~$30 a month. Lo and behold, this organization is fragmented and the team that gave the credit is different from the team that applies the credit. For some reason,the team that applies the credit messed up and have not been able to fix this issue. As a result, every single month I need to spend 90 minutes on the phone, justifying that they messed up, to which we always arrive at the same outcome "this is our fault, we will fix it, we will manually apply the credits this month, but it will be automatic next month and it won't happen again". Clearly they lied to me, since I have been calling them 12 months straight now, and every single month we go through the same drill, same speech, same dance, but nothing changes. I just got my bill for Sep and guess what, despite a supervisor promising last month it wouldnt happen, it's wrong again. I have so much anxiety receiving emails from xfinity it's crazy. 

This is literally the worst customer service ever and I can't believe I am still having to plead with them to manually fix it every month despite it being a problem longer than a year now. I deeply implore all of you to stop using xfinity, and of course if anyone had a similar issue I beg you to help me.