You need a key extractor, they're available commercially or you can make a toothed style yourself from an old fine toothed hack saw blade. Take 3-4 inches of an old blade and grind it down from the smooth side, almost to the back side of the teeth to the approximate length of your key. You'll have to make it pretty thin. You can take off all but a few teeth to gain a bit of wiggle room if needed. You can then insert the toothed edge of tool along side the toothed side of the key, it will push the pins in and the teeth will bite the key on removal and back it out so you can get a hold of it. Be sure to make the tool so that the teeth are oriented correctly, pointing up as you insert it. I have to use one at work from time to time. It should look kinda like this.