Man, I'd be super p*ssed and DW even more (being an accountant that counts beans very closely).
I would politely ask them if there is fine print somewhere that says they can do that and if the fine print was available to you at the time of paying for the reservations. If they didn't make you aware of fine print upfront that covers additional charges, I'd say they can't do that. Will they give you a refund, either in part or in full? At the minimum, it's definitely poor public relations. Can your BBB help?
I have no idea about other states, but Washington state supposedly has regulations on what RV parks/resorts can charge customers. I've tried an online search and can't find anything.
If you plan to do lots of camping, perhaps you might want to look into a membership type CG network. We are Thousand Trails members, and there are others. You will have a contract that is def. followed. We bought a top of the line pre-owned membership for a really good price and can use any of their CGs across the US. There is the initial purchase price and annual dues. We camp around 50-60 nights a year and the per night cost is very low and they never add additional charges. The only problem with Thousand Trails is they don't have CGs in a large portion of the central US.