Hertz Corporation Hidden charge of $38.31, no explanation, refunded without reason after complaint Maui Hawaii

I rented a vehicle online from Hertz rental. At the time of booking, I paid $187.83. I was supposed to be charged $81.28 at time of rent. I did not agree to any upgrade, insurance, or anything along those lines, and paid what I thought was $81.28 at the desk. The paperwork I was given confirmed this.

After returning the vehicle, I was going through my credit card statement and noticed I was charged $118.94.

I barely drove the vehicle - I only drove under 300 miles for the entire week (had unlimited miles), returned the vehicle with a full tank of gas, and didnt do any damage to the vehicle. What is the extra $37.66 for?

I inquired with Hertz on June 3 asking what this charge was for. They sent me 2 more emails after wanted me to rate their service and take a survey, etc. I took one of the surveys just so I could ask again why I was charged this amount. I finally heard back from my inquiry on June 10 with the following message: