Continuous Unauthorised Debit Order - Store & Call Center cannot assist

My Cell C cellphone contract finished in February 2018, so I sent in my cancellation form 21 days before as required by the service providers (had been bitten by this with Telkom before so this time I made sure) and further requested that the line be deactivate permananelty. As expected I got my last statement in March 2018 for the services in February 2018 which stated -R31.98 which meant this was an amount due to me. In April 2018 my account was debited twice by Cell C amounting to approximately R460 to my surprise I went to the bank to reverse this because I don't owe them anything (Each debit order reversal cost me R40 which effectively means I lost R80 from the two debits). I went to the nearest Cell C store where I was told that they cannot help me as my information is no longer on the system because I had deactivated the number and that only the call centre/customer care can help me. This then happened again in Yesterday so I called the customer care (Note that I no longer have a Cell C sim card so even the phone call to try and fix this is costing me money), after speaking with the lady from customer care for 10 minutes she could help me because I apparently the system says that I am giving her incorrect information. In my head she should be able to tell me which information is incorrect however I was told that unless I can give her all the correct information she cannot help me and we went through this question and answer thing about 3 times. Accepting that I am somehow clearly giving her the incorrect information and I cannot remember as its more than 3 months since my contract ended, I asked what is the way forward surely there should be another way to validate my identity and I was told the only way is if I h=give her all the correct information or she cannot help me.

I'm so frustrated with Cell C and would never recommend them to anyone as this isnt the first time we've had these sort of problems during the period of the contract hence I even deactivated the number permanently.

Sadly My bank has advised the only way forward is to close my bank account and change all my other debit orders to a new account or these debit orders will keep going off and cost me everytime I reverse them but I dont even know what they are for. What a nightmare!!!!!!!!