Avis Car Rental - Fine for expired License disk

I got a rental vehicle from Avis when my vehicle went in for repairs. One morning just after I dropped my daughter at school, I got pulled off at a road block. To my surprise, the Avis vehicle License disk had expired. So I did explained to the policeman that this was not my vehicle, but he still gave me the fine. So when I got home I contacted Avis and they actually knew that the license disk had expired, but they still gave me the car as their comment was that there were no other vehicles available. So they immediately swapped the vehicle for me and also promised to sort out the fine immediately. This already happened in February 2023 and we are now at the end of November 2023 and still did Avis has not sorted this fine. No one is even trying to help get this resolved and no one is even responding to the emails. Does anyone maybe know what I can do here, as I am not liable for this fine and surely can someone assist by getting this sorted.