Good evening my name is Prabern and I am having endless debit order issues with Cell C

Good evening my name is Prabern and I am having endless debit order issues with Cell C.I have been telling them to stop debiting my bank account as I was retrenched so I have been paying them cash on a monthly basis but they still suspend my service and when I contact them and show proof of payment they unsuspend my service. Everytime I phone the call centre the consultant don't understand simple instructions. Again my service is suspended. I was told previously if I don't want to be debited I must send my retrenchment letter and also pay cash 5 days before debit date which I do but still no body understands or do their job properly. Please assist. Thank you, Prabern ***