Don't pay the bill, let them take you to small claims and make complete fools out of them in front of the Magistrate, it is sport.
Avdata are leeches and a blight on General Aviation.
Fully agree - I got a bill from them to a Company that never had an aircraft at the East Aus field. They would not back off until finally I had matter shifted in the location of the Court to where it suited me [have to make application when you place the defence], then at the end they finally backed off - Amount $300
Give them HELL!!! and just pay the owner of the field.
I certainly do not have any responsibility to an organisation that I have not agreed to do business with in the first place.
Suggest you write to AvData and tell them that you have no legal arrangement with them and that you not authorise any arrangement.