Contract extended without my consent / permission

My contract with MTN expired in February 2021. Imagine my surprised when I got a call from debt collectors who informs me that MTN handed me over. So on Saturday I visit a MTN branch, whereby I'm informed that MTN extended my contract ... without my permission!!! When I asked to see the contract I signed for the extension, I get told "it was done over the phone" (which was strange, as my number has changed in the interim and the old number was a company phone). I then asked to hear the recorded call and again "sorry, we don't have it". Surely that is ********?!?!? Now they want me to pay R3000 in "arrears" before they will even cancel the contract I never extended! How can they get away with this?!?!?!