My Insurance want to charge me loads for cancelling my insurance can they charge this?

I took out car insurance just under 2 months (total approx �1400.00 ago and i'm paying monthly now my car is on its last legs and i can px it for a different 1 but my insurance want ove r �2000.00 bear in mind that im going from a 1.8 zetec petrol to a 1.7 standard diesel. I phoned up to cancel but they want to charge me over �300.00 can they charge that amount