Happened to me last week with ACI. Was short and they filed for ch 11. A number of things happened
1. Trading was halted for the full day that they announced
2. Trading moved onto the OTC markets (pink sheets) with a new trading ticker.
3. Couldn't deal on the online platform, had to ring up my spreadbetting firm directly.
4. Covered via that phone call
5. Got destroyed on the spread.
They claimed the price they had were getting was $0.2920 per share and they could cover for me for $0.3020 to include their spread. I don't believe for a minute the share price was that high, I was looking at an online quote which was coming in around $0.20 at the time. As I didn't have direct market access I couldn't really argue much with them, it was really take it or leave it.
Not the end of the world in the big picture of things, I was short since $4.00 so I was just keen to cover and take my profits.