Dotsure

My vehicle was hijacked in July and I'm insured with dotsure, am covered for full comprehensive. But they not paying the shortfall wich is a big amount, can't even get a new vehicle before I pay the remaining shortfall amount. My question is why are we paying insurance for a full cover ? For them to tell us they won't cover for certain things. They only covered the value of the vehicle I really would recommend dotsure. It will leave you high and dry. They telling me i was not paying for shortfall on my policy Wich is something they never mentioned that there is certain amount that I have to pay for them to cover for shortfall.