MTN Unwilling to Close My Account

MTN Unable to assist my wife with closing her account, this has been ongoing for 2 years now it is completely unacceptable, the arrears of the account were paid off in 2021, we sent confirmation for MTN to close the account and until now, the account is still running this has led to more arrears and the debt collection contacting us, I have never experienced such service like this ever, this mistake from MTNs side is affecting our credit score, my faith in MTN has diminished.