I would send a copy of my reservation and also a written letter saying you understand that the people wish to stay another month however, you have been spending the past 8 years there and specifically reserve that site because it is near your friends.
Basically your reservation states the site number and that was your expectations - otherwise why reserve?
I personally believe it's better to write or fax so you have some proof and it's harder to blow you off. If you write the letter send it with tracking - which shows when they resceived it.
Good luck.
