Vodacom has no customer relations. They are acting ********ly.

I am being handed over by Vodacom for an account for my son which the phone was fully paid up over 10 years ago. I discovered that a small monthly amount was still being debited despite not having been asked about renewing the contract, so I asked my bank to stop the debit order and phoned and sent emails to Vodacom. I never had a response to either emails or call, and was met with complete rudeness. Now again a few years later this has started again, having been handed over to a debt collection agency. What can I do please. I am desperate and totally frustrated. I have never had any supporting documentation to support the claims, just sms messages. Could this be a ****?