Incorrect Amount on Debit Order

On 06 October I had taken out a cell phone contract through a Telkom agent for the value of R 499. On 08 October my account was debited for an amount of R499.00 this is without receiving a copy of the contract neither the device. The device was received in mid Nov 2015. 6 December I received an account for R 994.90 which is now the incorrect amount to be debited to my account. I phoned the call centre on the 7,8 & 10 asking for them to correct the debit order, which was ignored. I realised It was going to deaf hears I placed a stop payment on the account until the matter is resolved. On the 5 January I receive a statement which now indicates the account is in arrears. I receive an sms for immediate payment of R 495.90, firstly I call the billing dept to check the amount the debit order will be for, I quote \ if you pay the amount of R 495.90 then on the 31 January the amount debited will be R 502.50 as long as the payment is made 10 dates before"To avoid disconnection I went to Telkom Shop for confirmation which they did. Made payment at ABSA of R495.90 returned to Telkom Shop they faxed thru deposit slip to billing dept. On 15 January 2015 I am debited for R998.40. """