Found myself in similar situation last week except I don't have a key lock on the boot. Stupid valet switch flicked itself somehow. Of course boot was full too. Had to remove back seats and inspection hatch, push all the crap around in the boot to make room and used a longish BBQ spit skewer to flick the switch back. I've now zip tied the carnt so it can't happen again. In your case once u have it open again I think u just need to clean the locking mechanism and lube of some sort. Good luck.