Telkom billing

I took out a telkom mobile contract in December 2017, up until February telkom didn't debit my account which was set for last day of the each month, eventually in the middle March dey hit me with Bill for R998 which went off unpaid. This happend 4times(each unpaid debit is R150) call center agents where useless departmental manager Shaldon, same. Number of calls where log n never once did I get feedback. Now once again same has happened telkom didn't not debit me for May n now hit me with a R504 bill on June 16th, a call was also log for this in store no response yet. who give these idiots authorization to changed debit dates with out informing customers. By dem changing dates, I had to bare the bank charge bill for multiple unpaid debits. Why should I pay those charges when telkom messed up.