Worst Bank ever

Two months ago I requested that my account gets closed as I am longer interested in bank with Fnb after being with them for close to 10 years, I was chatting to one of their Agents on the Banking app and I told her to close my account, I then proceeded to delete the App. TODAY I am seeing that the account is still active and now has a negative balance of R2400. FNB has to be the worst Bank ever!