You have my sympathies as you are now finding out the nastier side of insurance and the service providers involved. In short, if you have had the use of the credit hire car, yes you must complete the form. It would sound like the other party's insurer are challenging cost from the provider of your vehicle. It now gets into very complex areas of credit hire. Fill the form out, be truthful, do not be led by anyone from any company. If you feel you cannot answer any question, write that "as a layperson I am unable to comment". The provider should have advised you prior to providing the vehicle of your duties, asked your "demands and needs" whether you were "impecunious" or not. If they did not, you are not liable for any cost they cannot recover, they are. If you get stuck at any point and want to clarify anything, feel free to get back in touch with us.