Personal Loan Debit Order

Fnb Loans department triple debited me for my personal loan amount. It is very frustrating me because I have other debit orders that still have to go through my account. And their call centre agents kept on calling me while I have already made arrangements to pay them. The most irritating part is that they call you and asked to verify your personal details which I feel it's a risky because I don't have a proof if it's really Fnb calling. Once you refuse to verify they abruptly hung up on you.