If you have comprehensive coverage on your vehicle you should be able to place a claim with your insurance carrier for the damage your trunk received when the garage where it was being fixed was broken into.

If you did not have comprehensive coverage on your car that was being repaired then you can check with the repair shop to see if they have insurance in which you can make a claim since the car was on their property at the time of the break in.

Typically through garages have signs stating that they are not responsible for this type of damage if it occurs on their premises. If this is the case and state laws allow this, then you may need to speak to a lawyer to find out your rights. It may be that the person or persons responsible would need to be found in order for you to get repaid for the repairs your vehicle now needs to the trunk due to their attempted break in on your car.