Trade in not receiving credit for Iphone

I have not been receiving credit 29.99 monthly off my bill as promised for a 2 yr promo. The 800 # is no help they say they are "working for the customer. no worries , we are on your side  and you will get a email and credit confirming " LIES. The automated system still still wont show this . I'm not the only 1 this is happening too and suggestions show to report to BBB. The xfinity stores cant help . Can a honest employee or manager actually solve this problem its been a year. $700 credit just to not even get half of that . I would like out of this deal what can be done ?