Worst customer service

I called mtn last year October to give notice to cancel a contract that was ending in December 2021.an agent advised me that I do not need to put in a cancelation notice and that I should call a day before my contract ends..i told the agent that doesn't make sense, she then advised I call before the month of November ends so that I won't pay any cancelation fee. When I call I am told I need to serve 30days notice, and the contract will now not end on the 13 December but 31st of December 2021. Why do I have to pay for being given wrong advise by their agent?? I have been asking them to pull the calls and listen as this is clearly and agent error on their side.