New propane Lite gas bottle.

HELP.

I am currently staying at the New Forrest Centenary site. We stayed here last September and I was persuaded to change one of my blue 7kg calor bottles for the new 6kg propane lite bottles. As I still had some gas left in the other blue bottle I've carried on using it until it ran out and was then going to change completely to the red propane light bottles. Now this blue bottle has run out they will not change it here for a red propane lite bottle saying that they have to change 'like for like' and can't do it.I have looked at the calor website and it states 'Cylinders fall into two categories, and can be exchanged for another cylinder within the same category free of charge.' and both the blue 7kg and red lite 6kg are in the same group. What do I do now if the caravan club say I can't change it? I'm left with 2 different types of gas now !!!