Sloppy

I took a contract with MTN in 2019, and a router was included in the package. They told me it would be paid up in March 2021. It’s May 2021 and MTN is still charging me for this contract even after I called them to cancel and I even talked to them via Twitter about this mishap now. I called them and I was under the assumption that they had closed it as it stated in the sms they sent me after talking to their service champion but when I went to the store they said it was still active and I had not cancelled it as I thought. Why is it so tedious and why is it the customers responsibility to do this task? The price of data is already so high I can’t afford these kinds of mistakes.