Hello and thank you for your question.
If, as appears, you do not see any basis for this bill, you should not pay it.
I would suggest you write to them stating you have received the invoice and it is not clear to you what the bill is for. Retain a copy of this letter for your records.
Whether or not you are obliged to pay for the bill is not clear from what you have said, but they would be foolish to take legal action against you before they have first explained the legal basis for which the bill is payable. Either it should relate to work they have done at your or your agents request OR it is something mandated by legislation. In either case they should be able to demonstrate what they are charging you for and why, and it certainly is completely inadequate for them to simply state it is government policy. If they persist on that line, ask them to refer you to the relevant law.
If they do take action against you, then you should be able to show your letter asking for an explanation and their replies, and if a court thinks their explanation is inaduate, then even if you are found to be liable for the payment, they should have to pay the legal costs of pursuing you.
I trust the above assists.
Good luck and please rate my answer.