MTN's Incompetence and Harassment After Contract Termination

My contract with MTN ended in 2020, fully settled. However, in 2023, I'm receiving calls regarding unsettled amounts. I've emailed them thrice, but no response or acknowledgment. I have undeniable proof from THEIR programs showing I don't owe anything, and I don't even have an account. MTN's *********** staff and lack of resolution have left me utterly disgusted.