MTN trying to **** me if my money after settling account

So I run from Cell c all the way to get a contract from MTN to what I thought was a better deal. I got a contract from Mtn, last month I decided to settle it...called to confirm if payment was received and yes I even got an email with a paid up letter...but then MTN decide to debit my account again after payment,i asked for refund and they been processing it from beginning of December already now it's almost Xmas oko I been waiting for my Money instead I get another email telling me about a debit order that's going to go off again even before my refund was sent to my bank... I am sooo freaking angry with you guys coz I trusted you with my details....how dare u confirm receipt of payment and then continue to Rob me like this...I want my refund back and you better not deduct from my account again.