Vodacom cancelation

My father took out a Vodacom data package for my mother. He has dementia and they came to live with me. I tried to cancel Vodacom as my mother was using our data. Vodacom shop was unable to help me. I had to phone, but ran into al kinds of trouble because I do not have a vodacom account and it is only a data card, so I cannot use it to phone. Eventually I found a way to speak to a consultant who constantly wanted to speak to the 'account holder' (which I understand). After some months of going to and thro, I reached someone who said I must mail a letter of authority to act on his behalf, then they will talk to me. The email kept saying 'rejected by recipient', and I could not talk to the person again, she was either out of office or not available each time I phoned. Eventually got hold of someone willing to help. Cancelled the ckntract, but then they kept deducting for ceveral more months but at a lower premium. After that stopped, now several months later, suddenly there is Vodacom deduction. I am fed up.