Credit Card Charged wven after cancelling service

I was a Ringcentral eFax customer and I called and cancelled my service. Even after that my credit card has been charged for the last 3 months. After every charge I called to clarify the situation and the next month it happens again. I tried getting on chat with them but they ask me to call the customer service and when I do that the same thing happens again. I sent emails describing the problem and I receieve an automated email saying that if I do not contact Ring Central in 72 hours the issue would be considered resolved and the matter would be closed. I am not able to reach anybody with any authority to act. Every time I call the customer service I am connected to some offshore call center who promise to call me back and take some action but I never hear from them again, they put extra effort in being nice rather than effective. There process closes all complaints in 72 hours automatically whether it is resolved or not.

I have been contacting them every way possible but I got no results.