I haven't made a complaint, but I work within the complaints department of a major bank (currently on mat leave though). Have you tried contacting your insurance company/lender's internal complaint department yet? Generally that's the best way to start as FOS will recommend you do that first prior to lodging a complaint with them. Financial institutions have up to 45 days to resolve a complaint, but insurance companies have less. From memory it's 14 or 21 days. I have managed a few FOS complaints previously, and work closely with the team who deal with them, so I may be able to answer some questions if you like?