Avis and FNB lack communication and full of delay tactics

I had a rental car from them as my car was in an accident. On 15th January 2024 while my son was in the office, a bakkie reversed into the rental car. The company took full accountability. My credit card was debited by Avis for the full amount of the repairs and issued me a nil invoice. The third party's insurance now wants a letter from Avis stating that I did not claim from my insurers for the event, which I did not. However, Avis is resisting giving me this letter and I cannot fathom why!!!!

Despite numerous emails to FNB(who say they cannot issue me with that, which is odd since they are my insurers), I cannot get this letter! Delay tactics at their best. All I want is arefund from the third party's insurance for what I have paid out to fix Avis' car!!!