Unauthorised debits

Cancelled my contract with Vodacom via telephone and email on 26 January 2022 giving 30 days notice on a contract that expired on 26 February 2022. Cancellation was acknowledged. 1 April Vodacom debit more than double my previous monthly installment on my cancelled contract. I try call to find out what is going on and can't get any assistance as it tells me the number is now prepaid. I just received a statement today for an another installment after sending an email with all the correspondence confirming my cancellation. No response. I call their helpdesk billing department and keep getting cut off as soon as the operator answers the line.