Unable to reslove issue of Dubble Debit Orders

My sister has been a client of fnb for a while, there has been a very unpleasant experience regarding a dubble debit order, this issue has gone on for a while now. And no one can resolve this issue, certain accounts are debited twice, and that money is not seen anywhere. Now fnb is treating to close account or hand it over. How unprofessional is that? This will be taken further even if legal action is required, because this is a bunch of nonsense. Fnb is def not the best bank out there anymore!! Sort this out!!!