WebAfrica keeps on charging me for services cancelled on time

Good Day everyone I have had a contract with WebAfrica for 24 x months which ended on 31 May 2024. I have given notice in writing on the 6th of April 2024 (more than the required month) but they still went along and debit my banking account for services for the month of June 2024. In total, I have 14 x emails trying to explain the facts to them but without any joy. I have to keep instructing my bank to cancel their debit order as I cannot cancel it myself as the debit amount is more than R500.00. Then by the next month, WebAfrica again deducts the same debit order which was initially cancelled by my bank. WebAfrica does not stop and nor do they make any effort to understand the basics of this situation but rather proceed to overcharge me