disgruntled

How do we appeal against being charged interest for a late payment of Vat which was not on our account? I have called the vat helpline twice now to discuss this, first agent said the charges would be dropped as it was not our fault, however the amount is still showed as owing on our account. I called again today and got another agent who now says we must appeal about this in our online account, However there does not appear to be an option to make such an appeal. Can someone please inform myself the correct method to use. thanks