Wondering if anyone has any suggestions for how to handle this situation?

Had a confirmed reservation with Avis at a Miami location for pick-up this morning, but upon presenting myself at the counter I was informed that they had no cars available.
This was a 9 day rental booked several weeks ago for USD320.
They refused to provide any documentation that they were out of cars, and informed me that a car might be available this afternoon but not to get my hopes up, because of the holidays mayne places are overbooked.

Called Avis reservations who offered to make a new booking at a new price, but could offer no other help. Called another location in Miami Beach who told me they are also sold out, even though avis.com showed availability there.

We have booked a hotel in Clearwater Beach today so need to get on the road...
I have made anew reservation through Sixt, but have been unable to get through to them on the phone so unsure if they may also be sold out, but will soon find out.
Sixt rate was ~USD1300 vs the USD320 I had booked with Avis.

Best case I am USD1000 out of pocket, with some holiday stress to boot - can I expect any goodwill from Avis in this matter?
We are visiting Florida from Europe.