Fox Rent A Car review: Insurance that was specifically stated not needed

I rented a car through Fox for a monthlong work trip.
A week into my rental I saw that the charge from when I picked up my car was an additional $827.98 which from my understanding was a half a tank of gas and the deposit. This seemed rather high, so I called to ask why it was so high and was told that it was probably the deposit but they couldn't confirm since the rental was still active. The only way to know for sure was to go to the rental place. I was working 12 hour days and didn't have time to stop, I also thought it would turn out ok in the end.

Fast forward to after I returned the vehicle, my deposit returned was only $148.70. Apparently the additional charge was for insurance that I told her three times when picking up the vehicle that I did not need. I had insurance through my job. Now after calling and being given the runaround I'm being told that even though the site made some mistakes, they are upholding the charge and will do nothing for me. This is absolutely maddening. I feel like I have been scammed. This rental cost has doubled because of the insurance that I clearly stated I did not want or need and then am being told because I didn't come in during the rental there is nothing that can be done which I know is a lie. I am also frustrated that when I did call she could have told me it was for the insurance which would have made me do something while I still had the rental outstanding, but she didn't even though she could clearly see that on the invoice.

I am absolutely appalled at how you scam your customers and even after talking with the manager at the Las Vegas location where I rented and him telling me there was fault on their side, they are still keeping my money.