Contract not canceled.

Contact not canceled I would just like to make an formal complaint against MTN for treating customers unfairly. My contract ended December 2022,it was fully paid and I contacted cancelation to convert it to prepaid which according to the consultant it was done January I got an sms that I need to pay , I went to Maponya MTN store and I was advised to contact cancelation and I did that again and I was advised to ignore the sms as the account is now on prepaid and is paid up.to my surprise this month I got an sms of an outstanding amount and a threat to be handed over.i called MTN and my account is still on month to month contract and I owe MTN for the mistake they made of not converting my device to prepaid and listed on credit berau for defaulting.

Should this not be fixed am going to Escalate to the ombudsman.