Complaint wrt interest reversal

I am beyond frustrated and disappointed in the service I am receiving from FNB trying to get interest reversed that was charged incorrectly on the 26 Nov due to a system fault. I have queried this on 5 occasions, the last one on Monday 21 December when I recieved a call and promised it would be resolved and I would get feedback. It's now the 24th December, no reversal of interest nor any communication- absolutely disgusting!