Nightmare router and wifi contract

Worst customer service ever. I had a 2year contract with them for router and wifi. When it ended they asked if I'm going to renew I said no. I was paying R230 every month, contract ended in October and in December I hot an sms saying I've been handed over for collections and that surprised me because I didn't owe them anything and our contract had ended and it's not like they contacted me before about the debt that I "supposedly have" with them. I've been getting calls from debt collectors ever since for something I don't know off. They claim that I was supposed to call mtn to cancel the contract, something I was not told in the store when I took the contract. And I called mtn in January to cancel after the debt collectors told me to but they send me pillar to post. I don't know what to do anymore in order to be rid of them and I can't pay for something I didn't use. They claim that they've been loading data to my router, they've never stopped after October which is a lie because if u don't pay they switch off your data immediately so now why would they load it after my contract has ended? That router has been not working ever since. They're the worst decision I've ever made