Avis Car Rental - I swear I opted out of extras but was charged for them

I just booked an AVIS car rental the other day, and swear I opted out of the extra charges (insurance, tolls, etc.), so of course once I hit confirm, I didn't check the agreement that was emailed to me, thinking all was well. I don't usually rent through AVIS, by the way. However, when I called today to extend my rental, and looked at the agreement, I see that there are over $800 in additional charges for my rental this week for all of the "extra's". I explained to the person at the location (over the phone) that I was under the impression I opted out of those. However, she said since the rental was already pickedup and in progress, there is nothing that can be done. I did some research (because of course now I'm ticked off and out $800) and found where other people have had similar issues. I plan to call corporate tomorrow and ask for a post rental adjustment, but have no idea how that will go. By the way, did I mention I booked this for my manager, so it's not like I can go up to the counter at the location and argue this in person. Nor do I want to put that on her to argue in person. Of course I made her aware of this, and told her I was going to fight it. Any help on how to rectify this, or any stories of other people having a similar issue on their website would be helpful. I'm so aggravated. Where of course I don't want my manager to eat these additional costs, I have offered to pay for them. But I sure as hell don't have $800 sitting around! Ugh. Frustrated as all hell.