Claiming warranty on Xperia 10, should I reflash Android, lock the bootloader?

I accidentally dropped my Xperia 10 II and the screen broke.

Contractor (Sweden) says that a screen replacement would cost just over half the cost of a new phone but since I’ve unlocked the bootloader they would need to replace the motherboard and that in it self is more expensive than a new phone. They also claim that my insurance will not cover this since the fault (unlocking bootloader) was caused by me.

If had not unlocked the bootloader and the phone was actually beyond repair, my insurance would cover the cost of a new phone.