Worth checking whether the garage has any closed circuit TV. It's a long shot here, not like the UK, but you might be able to see who has caused the damage.

If you've got full insurance, you should have coverage for the damage. Get an estimate for the cost of repair, and weigh up the pros/cons of claiming for damage. If the payout will be really small, it's probably not worth claiming, as you may lose your no-claims bonus and face higher premiums in the future.