Have received a reply from Hertz:
After reviewing the charges, we have determined a credit is due. An adjustment of $12.00 is being processed to the account billed. The adjustment is being made at this time, but may not appear on the next monthly statement due to billing cut-off dates.
Thank you for bringing this matter to our attention. We appreciate your business and look forward to the opportunity of being able to serve you again.
It's good that Hertz Corporate is able to process the refund. Not planning to write to them about the Counter Agent - if there is another occurrence, then will consider it.