Does the knob still twist back and forth ? On my 79 the knob twists "counter clockwise" to open.....when the door is shut its harder to twist than when it's open, be sure you have it twisted all the way to the left, try pushing in on the door itself when twisting the knob...when it's open it's spring loaded to closing position..mine always sticks a little because it's left edge rubs a bit on the plastic of the center console piece. Once your sure it's twisted all the way to the left you can try gently prying with a plastic tool...
If you get yours open you can check to see if it's rubbing somewhere first, then try aligning it or tweaking the hinges...possibly wax or apply silicone to the edges, also check the latch itself, perhaps it needs to be tweaked..
Let us know when you get it figured out, and good luck! P.S. hope you find a big stack of money inside when you finally get it open!