Try cutting an old inner tube up, put a small piece between your vice grips, it'll hold the shaft better. The nut will always be way inside the top mount so unless you have a special tool, all you can use is a deep socket or an impact driver. It can be the same problem doing the bolts back up, so make sure there's absolutely no play in the top mount to bolt before putting back on the car. Even a mm missed in tightening will result in a clonking, tapping noise. Be careful also not to tighten up so much so strip the threads, I did this and then bought a new damper! Very probably a bad idea, but I had to grind some spanner flats into the very top of the damper rod, (where the bump stop covers) otherwise I couldn't shift the nut.
Either take it to a pro or buy an impact driver.
GT 3.2 V6 - Q2, KONI FSD & EIBACH PROKIT, GTA REMAP, MICHELLIN PS3's, BMC CDA
159 SW 2.4JTDM TI - ALFATUNED, WIZARD BACK BOXES, KW V3 COILOVERS, NOKIAN WR A3/MICHELLIN PS3, PCA DYNAMICS ALIGNMENT.