You need to separate out your rights with the airline from those with your insurer.
The airline was obliged to provide you with a full refund OR an alternative flight. (It's not clear from your post whether you took the refund and then booked completely fresh flights or whether you accepted a replacement flight two days after the one you'd originally booked).
IN ADDITION, unless the flight cancellation was due to circumstances wholly beyond the airline's control, you're entitled to €250 compensation if it was a short haul flight. (€400 for medium haul flights or €600 for long haul):
https://www.caa.co.uk/Passengers/Resolving-travel-problems/Delays-cancellations/Cancellations/Short-haul-cancellations/
What, if anything, you can claim under your holiday insurance depends entirely upon what the small print says. Some budget policies might not provide any relevant cover, whereas other policies might pay out for the missing days.