Number Porting Issue From FNB's Side

I went to MTN to take out a contract, but I wanted my number to be ported from FNB. I was on a 2 year contract - my last debit order was the 01/02/2019. I have received an sms that my number cannot be ported I need to contact my service provider - so I phoned FNB. The lady had advised me that I need to cancel my sim, and it'll take 30 days for cancellation. I told her that my contact ended in February - she said for the device but the sim carries on until I cancel. Now how is that possible if FNB didn't deduct money from my account on the 01/03/2019 (my debit order date) and I didn't received any data and voice data (which was my contractdeal in the beginning). So therefore my contract is prepaid. Even when I log into my internet banking there is no info pertaining any smart device or sim debit order.