so here it is-- their answer... not really sure what it means are they going to credit me back at some point??

Thank you for contacting Avis Customer Service regarding the reservation
and rate applied. We apologize that the charges displayed in your
reservation records differed from what you were expecting and we will be
pleased to assist with your concerns.

Upon reviewing our records, it appears that the reservation web-page had
a glitch at the time of reservation and a higher rate was applied to
your contract.

at this moment our systems do not allow us to made modifications in
order to modify the amount due that is showing in your reservation.
Because we value your business, we will apply the rate from reservation
xxxxxxxxx, resulting in a no charge since you have already do the
prepayment of $18.91 for the original rate, this will have to be process
until the end of the rental once the system have close the contract and
calculate the amount due in order to do the adjustment. Once the
contract is closed please allow three to five business days for
processing.