Green Homes Energy Grant Sub Floor and Solid Floor Insulation

I have been trying desperately to get through to the government-approved list of trusted contractors asthey've been inundated. The two thatdid respond wanted £90 survey fee non-refunddable! Martin Lewis Money Expert says to steer cleearof these people. I have 4 rooms with 3ft void under the floorboards. It's an old house and very cold. I also have solid concrete floors in my bathroom and kitchen and no insulation so it's very cold in my 1 bed ground floor flat in Ilford