Unauthorized debit orders from MTN

I am so disappointed with MTN, I had a phone contract with them which ended last year May.. I called them more than 3 times, even went to their store to stop debit orders from running.. They promised that it was cancelled but the d/o is still running even today.. The number is not even working anymore but they're still debiting me.. It frustrates me, I regret why I didn't t go to a different store..