Terrible contract

Mtn has been absolutely awful since the day I started my contract. They first started by not debiting the money from my account and then would block my phone. Then even after paying for my contract EVERY month, they would still block my phone. They now say I'm owing close to 900 bucks, I've sent my proof of payment, I even went into the store and showed them the proof and they wouldn't help me. Not to mention that the other teller was extremely rude when I wasn't even talking to her. I did this contract at Clearwater Mall and I honestly regret it everyday