I have trouble using the keys on both my cars, it maybe lack of use due to remote entry use. I've found I have to firmly and quickly flick the key back and forth to get it to work, a firm slow turn doesn't seem to work. Try it, you appear to have nothing to lose.
If trunk is empty you might be able to move the valet lock, or attempt to operate the seatback release lever by inserting something between the rear seats.
Good Luck.
