Im extremely unhappy with NDA

Hi I made my last payment last year December and after a week or two I enquired about my balance statement which I got and it stated that I'm not owing anything, but hyphen was still going to deduct funds from my account for the assured life cover which I'm trying to close... I was happy and ecstatic with the fact that I'm debt free but my joy was shortlived, I got a call from standard bank sometime in January this year, I had a chat with them and apparently I'm still owing them R22423.06, i don't know how is that possible because I was paying money every month,never even skipped a single payment..

I sent nda a text on one of their communication portal, I got no response and I decided to call them and find out what's wrong, guess what, they told me their system miscalculated the figures and I'm still owing...

All this doesn't make sense to me because when I enquired about my balance statement nothing was picked up.

All this comes up now when they have to give me my clearance certificate.