Telkom mobile charges for their own mistake

So, I had 2 telkom contracts, In December the one expired. So I contacted them on the online platform to cancel my contract. They contacted me telling me that my one contract has not expired yet so I told them I will end it as soon as it does. They went ahead and charged me R1137 for Device Obligation / Carryover now that will go off at the end of the month. How can they do that, never have they told me they will charge unknown charges on my account. I contacted them just now on their online platform and they told me I cancelled my contract before it expired. I can't call them because they don't have an active line, all lines lead me to a whatsapp group that is no help at all. This is a joke. Telkom will never stop with the bad service. I was ready to take out new contracts but seeing this, I will stay away from telkom. They don't have a clue how to work with customers