Fnb negligence

I received a debit check mandate from isabellagarcia, i rejected it when fnb send it through…

Now isabellagarcia debited my account and since I rejected and never signed with them i thought matter is laid to rest

Only to see even with rejected mandate fnb still allowed them to debit my account now i have unpaid item that i paid unnecessary

Im given an excuse that if they have my account they can debit, fnb ive been your client for year I expect you to protect me