Avis/momentum vehicle hire

I had rented a vehicle with Avis in 2018. I requested a supercover insurance. I was informed that it was not available. I got the vehicle anyways. Unfortunately the vehicle was damaged when I returned it. I was charged an amount to fix the vehicle. Later on, I was told to pay more as the internal damages had increased rhw amount of liability.

I disputed the claim.

Now today, my insurer Momentum is hiring a vehicle for me as my car is in for repairs. Avis is asking me to pay the outstanding amount before they could give me a vehicle.

I have an issue with that as Momentum only does with business with Avis only...and I need a vehicle.