I'm not sure what your tool of choice was, but most people have recommended using a ball-point pen. With that in mind, you still have to be careful of the depth level that you push the pen in to make the holes. Ideally, you'd just use the very tip of the pen to slightly puncture the material and move the pen around the inside of the hole to open in up. When moving the pen around, one has to be careful to be mindful of the depth of the pen so it doesn't sink into the hole too far and damage the driver.
From the way it sounds, you might have damaged the driver. I've been there, done that. You might have to send your 'phones into Grado for replacement of the drivers. Their repair costs are not too bad and it will take about 3 weeks of total time - including shipping both ways.