Incorrectly Billed

I have been working on getting something returned to my credit card that has been incorrectly charged numerous times with over a dozen phone calls andpeople promising that it is being done and then no one ever following through.  During this process I have been asked if I wanted to upgrade my cell phone and TWICE I have had my service disconnected by the agent when I have said no.  A manager also changed my internet plan without my knowledge or agreement and i didnt find out until I got an automated email welcoming me to my new plan.  I am exhausted from trying to get this resolved and I have been met with empty promises and an unwillingness to help by agents and other managers.  I need a number to someone in the corporate office who can help me and listen to the experience that I have had so far with the company. I have been an Xfinity customer for more than 6 years and I am at a loss as to how to get someone to help me.