Unreliable service from fnb

I was called by someone claiming to be a collections company on behalf of fnb. Ive been trying to contact fnb since yesterday with no success to confirm if my loan account was handed over to a collections company. Those people had all my account information and all balances. Its so frustrating when you try to contact your bank to report such issues there's no way to getting through to them. Ive tried all platforms with no success.