Europcar claims for damages that consumer is not responsible for

I hired a vehicle from Europcar via my insurance in July. A few days after returning the vehicle, I received a call to enquire if I had hit a pot hole. I responded no as this was definitely not the case. I was subsequently billed with damage to a tyre (bubble and a nail) as well as damage to the luggage tray. I raised a dispute with Europcar and pointed out that the person inspecting the vehicle on collection already had issues opening the luggage tray to inspect the spare and jack etc. In addition I did not encounter any loss of tyre pressure due to an alleged nail being found in the tyre. 5 months later , I'm being threatened with legal action and being forced to pay for damages which I'm not responsible for.