Before you can go to the Financial Ombudsman Service you need to complete the insurers complaints process. If you check the insurance policy this should state to whom you should complain in the first instance, be it either a Complaints Department or the Managing Director. Your complaint has to be acknowledged within 5 working days, and subsequently thoroughly investigated. Either the insurers will find in your favour, or if not send you a final response. After this, if you are still not satisfied, you have recourse to the FOS, whose contact details will be on the policy documentation.