I'm not sure you completely understand the concept of margin...

I'm not sure you completely understand the concept of margin calls. If IG Markets lent you money to buy these shares, which they did, they take security over those shares. If those shares have been in a suspension and is reasonable to expect that they will have little or no value upon exit, how will IG recoup its loan to you on worthless shares?? I'll answer that for you - by taking those shares AND the difference against you. You may keep those shares but IG's security has suddenly evaporated, so it will ask for more. Margin lending is full recourse against the investor. They are quite right to do so. It's nasty but that's how it works. Good luck.