Paid twice for overcharged data usage

Got a massive bill from MTN for data usage when I thought my data usage was capped by my contract monthly amount. Cancelled the account and was told I needed to pay the outstanding balance by eft which I did despite being very unhappy that my data usage was allowed to escalate with no warning from mtn when I thought it was capped. Then after I reluctantly paid by eft to get the account closed. It took weeks for mtn to actually close the account and convert the numbers to prepay and on top of that mtn has now taken the amount by debit order from my account. Have spent the last two weeks trying to get a refund but all I am getting is ******** from mtn. A greedy company with terrible customer service who have basically ****** money from me and se to by trying their hardest to hang on to it!