The first 2 days are a no brainer. They failed to provide you a place in their campground that you paid for.
The remainder is a bit muddier but you should be able to claim that you had to get a different site since they failed to provide a site at the start of your visit. The counter claim would be it was available for the later part of your trip.
I would ask for the refund and argue a bit. If they don't give in and you paid via credit card, I would file a claim with your credit card company for them failing to provide the service paid for. Baring that it's not worth getting a lawyer involved or taking them to court.
Tammy & Mike
Ford F250 V10
2021 Gray Wolf
Gemini Catamaran 34'
Full Time spliting time between boat and RV