Do not take a contract. They are ****mers

Please someone please explain how a phone contract works with Vodacom. A phone my mother bought in 2016 which she finished paying it off because it was a 24 months contract which by the way the still debited her till 2020 till she changed banks. Now she’s receiving threats that legal action will be taken against her? How?! We have receipts unfortunately bring it on. You guys underestimate people. I swear if we get one more phone call or sms I promise you I will sue you. Stop harassing us and do your jobs