Debit order

I had a 6 month contract with MTN for R488 per month and the contract ended in December 2022. I was informed in an sms that I can continue month to month subscription for the amount of month to month R293.56 as the router has already been paid. I received another sms the afternoon informing me that the debit order is R511.54. I sent an email to MTN on 5 January 2023 in which I got an automatic reply with a ref nr. that they will reply within 24 hours. It is almost a week and the debit order was deducted. I get no response and when I call 135 I get automatic replies and no one to talk to. This is unacceptable as I have not given any consent for R511.54