Xfinity does not correct their billing error

I signed up for Xfinity basic internet service when I moved to a condo. The Xfinity contract quoted a sale price of $45 per month. But Xfinity has kept billing me $89. When I inquire about what is going on, I am told I have home phone service through Xfinity and that is why the bill is high. But I  never signed up for Xfinity home phone; I have Ooma. The agent will say, he/she can certainly take the home phone service off my bill. But the next month, the same $89 bill arrives, and I call again. This has happened 3 times. Last month I again contacted customer service and this time got an email confirming that a change had been made and my bill would be $51 per month (I will settle for close enough at this point). But, once again my February bill is $89. It's hard to say what is going on. I will assume that there is simply a problem in  coordinating inquires in the system.

Please correct your errora and refund my overpayments. I think I've been patient, but I am about to involve the attorney general's office.