double debited

I have a top up contract with MTN and I pay R450 per month. on the 1st of November they debited R920 on my bank account, and I dont know why.<br> <br> This is where the story started, on the 1st of October the debit oder of R450 was rejected in my account due to insufficient fund, then i got a masage saying I must pay R480 directly to to Absa bank. on the 18th/ 19th of October I went to the bank and pay the R480, and MTN has confirm the receipt of the funds.<br> <br> on the 1st of November 2015 they debited R920 on my bank account, when I call the call centre (808) I was told that they are also including the amount for October that was rejected. i ask them why they including it because it was mannually paid to the bank? i dont get the cleare answer. i then called the following day with the hope of geting the second opinion, the lady at the call centre told me that they made a mistake , they will refund me within 5 days. after 5 days there was no refund , then I called the call centre again, they told me that there will be no refund, i dont get the proper explanation as to why there will be no refund.<br> <br> Im appealling for a proper explanation and the refund of R450