Over charged and bad service from customer service

I recently took out a contract with MTN late November during the black Friday and been having problems with the billing, being over charged every month and been calling to report every time I have been told it's been escalated and no one gets back to me I have references for my calls I also sent an email to customer service and was told the issue has been resolved but still nothing I suffer now cause MTN takes extra money affecting all my other debit orders and my credit record, today I tried calling to cancel the contract still they did not want to help me and was told to go back to where I took the contract which is 550 km from where I am please MTN can I have my money back and stop destroying my credit score I want to buy a house this year.