MTN please help

I took a phone with contract in March 2021. I was not informed that after setting an amount i was owing i must personally come to end the contract. I then finished paying in March 2023. After few months i received a call that am owing when I ask how? they said it because they were still sending airtime and data to the number which i was not using becouse am not used to using MTN number. Which means i was suppose to come at MTN shop and end my contract. I then made arrangements on how to pay, made sure that i pay every month. After 6 months i received a call again that am owing and am now blacklisted. Kindly assist