My debit goes off on the last day of every month

My debit goes off on the last day of every month. I paid R1895 end of March. Two weeks into April I couldn't use my phone. It was locked. Tried to call Telkom. You can't get through to an agent. They direct you to a watsapp line. The options don't allow to get any joy. I put a message on Telkom complaints on Facebook. The agent tells me my credit limit is R2300. My invoice was R1895 which was paid end of March. She tells me to pay R720 . Doesn't make sense. I was left stranded without a phone. Couldn't get a Uber home. Had to walk home like 7kms to get home at 6.15pm . No explanations. So my debit goes off on the last day of the month. Today is the 1st and my debit hadn't gone off. So now my account will get blocked again. I'm not the only one. There's so many people experiencing the same. We can't get through to Telkom