No customer service

Hi, I really do not know what to do anymore... This number ***) was incorrectly upgraded, it was cancelled and the phone was returned on 8 May 2023. But I am still getting billed for this contract. I phoned so many times now and it is not getting resolved. When trying to talk to the billing department now I received a message saying my number is blocked due to the amount of times I called Vodacom.... how else must I get this resolved as my next step will just be to stop my debit order. Regards Werner