bill credits

I've been having an issue with CS where I was promised/guaranteed a credit amount for my bill and it would reflect onto my account with a specific timeframe. When I did not see the credit I contacted again as told to wait more time and I would receive an email. This credit was supposed to be a full credit to reduce me bill that was grossly enlarged; however since it never was applied my account occured multiple fees even though agents continued to agree that the credit will be onto my account; they agents find a way to issue smaller credits while billing me 2x the previous credit amount.  Every time I contact CS they avoid answering any questions and just toss me between two different departments wasting hours of my time hoping that I either disconnect or just give up.  When I ask for a supervisor they usually try to help a little and start promising big but nothing ever happens; I've spent more time with CS than with working service and in the midst of the problems the agents try to upsell me on products and if I don't want the product they disconnect or transfer me w.o consent or worse try to bill me for items/products I never requested.  Then whatever happens on the bill the next agent just says the your bill is "correct" and there's nothing they can do about it.  or they try to create an issue.  I never expected I would have to create a forum post but seems like this might be the place to actually get assistance with  my bill.