Your post probably needs more information in order for others to provide meaningful advice.
At what location was this? What was the return process? On return, was there a Hertz representative to check and receive it. Rental receipt - where is it? With Hertz, these seem to be emailed shortly after the return, as a matter of course. Certainly in SYD and BNE they are not printed at the point of return.
In any case, I don’t see how this has anything to do with VA.
Edit: Sorry that I cannot help further, but you need to follow-up on the receipt. Perhaps the vehicle was not properly returned/checked in and the records show that it was still in your possession.
Was it at some place where there’s no-one to actually receive it and you did a key drop? Did you leave the keys in the vehicle and walk away, potentially allowing someone else to drive it?
Also, what prompted your concerns? How did you discover that there is a problem? More information is needed.