Telkom Theft by Debit order

I have a signed contract with Telkom for them to provide me with LTE service for a fixed price of R 249.00 / month. This contract has been in place since November 2017. Every month Telkom withdraws more than this amount. I then have to go into my bank and reverse this withdrawal and pay the correct amount of R 249.00 This month Telkom added R 202.70 to my Bill due to "Payment rejection Fee" I would strongly advise everybody to be very cautious in giving Telkom the authority to exercise a debit order against their account. Their Call center is unable to resolve this problem and advises one to just "pay the requested amount." This is theft and one cannot address it with anyone who is able to resolve it.