Fnb personal loan paid up but debit order still going through

Paid up a personal loan i took on the 02/8/2019, i personally called fnb back on the 25/9/2019 and received a settlement letter that stated i had paid up the personal loan but until today i am still been charged by fnb as the debit order is still going through, causing an inconvenience as i have to call every time to try and get someone to assist, today I was told all the supervisors/ team leaders are in a meeting and there's no one to assist, i have to call back, at my own expense. What kind of service is this? Why is the debit order still going through, affecting my credit profile and it even shows that the account is in arrears but dont owe fnb and i cant reverse my money. Please help