You can make a cancellation request from the "Bookings" section of your Click&Boat account. Click on "Access" then click on "Cancel booking".
If you subscribed to Mondial Assistance insurance at the time of booking, you will find your contract under "Bookings" > "Access" > "Mondial Assistance Contract"
Your insurance number is 303301. You will be asked for this number when starting the claim procedure.
You can send your request to Mondial Assistance regarding the cancellation of your booking through THIS LINK.