Aggressive retention tactics with the elderly

My mom's contract which I'm helping pay was due to be cancelled in August. Every time she queried she was referred to a very aggressive retention team doing everything in their power to sell her on anything other than prepaid. The person even said she'll lose her number if she goes prepaid and I know this is proper *******. Anyway, we get the whole ordeal sorted on the phone and were promised sms's and emails and all sorts of confirmation that the contract is indeed prepaid now, but now we received an account of over R700 and the phone is cut off. What the heck Vodacom? You guys are taking advantage of the elderly and the conflict averse with your aggressive retention tactics. I want this sorted before the sun goes down!