How to get a credit for cancelled service

I have called multiple times and have yet to receive a credit I was promised.  This last lady I spoke with just repeated herself saying her same statement over and over like a robot.  She would not do the needed research to see that I signed a new contract removing phone service from my account.  I was charged the service the following three months. I ended up canceling my entire service and was promised a correction in the system and refund.  I have yet to be taken care of.  I am really disappointed and would like help with someone not from a call center that could careless about me as a customer to assist me with my refund.