Telkom Is Trash

I opened a sim contract with Telkom for 10GB evry month. IN March they debited the money, however in APril they did not. According to them my debit order for March bounced back and two days later went through. There were penalties for that as a missed payment and when I advised them that I had money in the bank and had nothing to do with what happened they still told me to pay the penalty fees. In May they suspended my account, I called in and asked the lady to cancel my contract because for both these incidences that occurred, I had nothing to do with them. Even offered to give them my statement for March and April. The lady that was assisting me made a note to cancel the contract but did not escalate the matter to the relevant dept. When I called in last week to inquire about why I am still getting billed for the contract to-date, they informed me that the lady didn't escalate the matter so my contract is still running and I must pay for all those months that I have been billed for. I don't understand how this is my fault and why I am made to pay for a contract that I had asked to be cancelled in May. Why are they not taking the matter with the lady that was assisting me and find out from her why she only made a note and never escalated my request? This telkom contract is now messing with my credit report as it shows as missed payments. I do not know how to resolve this matter anymore.