Waiting 2weeks for a simple letter

I have paid off and closed my credit card. I need the closure confirmation letter very urgently. I have been trying to get it for 2 weeks now. I phone every single day and every single day, they request it and escalate it... Only to fiiiinaly find someone yesterday say there's still an outstanding amount. I paid this and now start the process of trying to get the letter. I'm going to lose my homeloan if I don't get this letter. Every person I speak to will ensure I have the letter within the hour.... But I don't get anything. I'm at the point where I feel like closing all my accounts with fnb because they don't want to help me with something as simple as a letter