Does the key insert fully into the lock but simply won't turn? Or does the key insert all the way and turns fine, but the door simply won't unlock? Or is the key not seeming to insert fully into the lock?
Maybe you were given the wrong physical key for your car. Maybe the key is damaged. Do you have another key you can try, such as the brown valet key?
Provided the linkage is still intact and I've tried every key I had with no luck, I'd probably spray some penetrating oil into the lock to see if that unsticks a possibly frozen lock.
Beyond that, you might try to access the rear hatch lock from underneath to try to release the hatch to gain entry. I've never done that before and have no idea if it's even possible, but I have seen it mentioned in othe threads. I'm assuming the 2006 hatch doesn't have a keylock underneath that isn't visible looking straight on at it. Peek up underneath where the release handle is to double-check there's no lock. Honestly, in the 18 years I had my 2003, I never really paid attention to the underside of the hatch, so maybe there's a lock that I never knew about.
EDIT: BTW, I mentioned trying to gain access via the hatch because in your other post made around the same time, you said you can't gain entry into your car with the fob and that you're having some immobilizer sensor issue. Not sure if that's still the case, or if you were able to finally get into the car using the fob, and you're now just wondering if the key is supposed to unlock the door. Yes, it's supposed to unlock the door and it will even activate the alarm (I believe) if the key is kept in the locked-turned position long enough. Turning the key the other way and holding it in that position disarms, unlocks, and rolls down the front windows.
You could use a plastic, rubber or wooden wedge between the upper door's window frame and the roof to force a space. Using that space, you could insert any number of long, skinny items to try to nudge the locking lever over to the unlocked position. I've done that before with other vehicles, but you have to be careful not to wedge so much that you break the window or damage the window frame so the door doesn't seal properly. Even a long, narrow tree branch that has a smaller branch on the end might do it. Requires a bit of imagination. Look around your home for anything long and narrow that might work, and that you might have to tape/clamp something like a metal corner bracket to in order to get the angle needed to nudge the locking lever.