Day light ******* by MTN

I am struggling to cancel my MTN month to month, I called to cancel end of March, I was told my contract will come to an end on the 30th of April, I took the router back to MTN now I'm getting an invoice for the month of May. I call to check I am now told the contract was not cancelled there is just a note on the system that says I want to cancel, I am not sure what does that mean. I paid for April and I did not even use their router and according to them I need to pay for May as well. I think they are ****ming people with this month to month nonsense.