Frustrated over billed customer, ******* service

MTN your service terrible, you have been over billing me for the past six months, each time call, I’m told it will be rectified but each month you debit me more than what my contract should be. When I call service, the line, your agent either drop the call or tell me they escalating it but each my months the invoice is incorrect and I am debit more than I signed up for. This is *******