insurance problems

help i need some advice.ive been driving 22 years,the last 12 ive had a diy camper as my only and everyday vehicle on a social,domestic,pleasure policy with scenic budget motorhome insurance.i had to scrap the van last year and have just got and insured a renault clio with octagon for £270 full comp.now 3 weeks into the policy they,ve told me that my proof of 6yrs no claims bonus is no good as it was earnt on a motorhome.its knocked me sideways ive never heard of such nonsence.i paid the full premium on credit card and cant believe they are going to cancel my policy with probably keeping half of it no doubt.
is this the law or something?theres no mention of this before you pay.what can i do,thanks in advance for any advice,rad