if the key closed it, it should open it...be sure to try and turn the ket while pulling the door to you or pushing the door away from you. it sounds liek the bolt is tight up againt the hosuing in the frame so pushing or pulling the door a mm should give you the room for it to open.
And the advice I was given by a lock smith....if you can see the bolt...and in your case you can, he said what he would do is get a hacksaw balde, a pair of strong gloves and you will cut through the bolt on a basta type lock in a coulpe of mintes. The brute force is extremely awkward as there is a good chance of you damaging the frame and the force should really be applied by pushing rather than pulling...if you pull the handle too hard you'll just rip it off the door in my opinion...