Need help getting billing credit

I have been getting the run-around and need a way to further escalate my billing credit issue.
I have chatted with multiple agents and spoke on the phone with multiple agents over the last few months. I thought this issue was finally solved and was directed to take the ticket number the last agent gave me to my local store to have the credit applied to my account. When I went to the local Xfinity store, I was told they could not do anything about crediting my account, that the agent I spoke with must have assumed I was going to go to a corporate Xfinity location (which is several hundred miles away). I was then told (at the store) that I would have to contact someone by phone, again, and have them credit my account.
When I spoke with someone again today, I was told I could not get the full amount I am owed credited to my account, that he could give me a fraction of the amount AND it would have to be broken up into multiple credits that I would have to call about EVERY month to have added to my account. I told him this was unacceptable and that I needed to speak to someone else. He told me there was nothing else that could be done and that he would add $30 credit to my account today, which he went ahead and did. $30 is a tiny portion of the credit we are owed. I have never been as upset with customer service as this call made me.
I need someone to fix this situation as soon as possible and not have to drag this out for months and months. Please, help me sort this out!!