Outstanding paid up letter - 3 months and still waiting

I have paid up all my debts with FNB in May 2021, I have not received my paid-up letter for my overdraft account, after requesting it numerous times now. Debt Rescue said that the account is in credit (don't know why as I paid the exact amount requested) I need the final letter so I can go forward with my clearance certificate. I have submitted banking details for a refund but no one is getting back to me, when I call they transfer me from one department to the other, when I go into the branch they just put me on the phone again. I need this to get sorted ASAP, point me in the right direction, going for month 3 now.