Cancellation of Telkom debit order

My son had a Wi Fi data package with Telkom. At the completion of the contract in September 2019 he cancelled the contract and received written confirmation there of. He has since accepted a position outside South Africa. Due to the time difference he cannot communicate with Telkom during their normal working hours. Since November 2019 Telkom has debited his bank account with the original deduction amount. Every time he has to contact his bank to have the debit order reversed. The next month the same thing happens again. We have been in contact with Telkom (telephonically, by e mail, on their website complaints section - there does not appear to work human beings at Telkom because nobody is prepared to talk to you) Every time we receive confirmation that the debit order has now been cancelled but it is just deducted again the next month. In February all of a sudden a new increased amount is deducted twice. The whole process of having to reverse these amounts have start again. The bank is most helpful but apparently Telkom changes one digit on the debit order and the debit order is automatically processed. Most frustrating and unacceptable service ever. If anyone can assist me in resolving this problem it will be appreciated