Not to defend them, but I have been trading with them for three years or so and I find them a very serious company.
As previously said, I believe this situation happened because of the news coming out of the rocket launch by Israel.
It is unfortunate that it happened to you but it is a risk we all have to bear in mind these days. With the proliferation of HFT, the machines get turn off automatically when this kind of volatility appears. As most of the trading is done by machines these days, it leads to an instant collapse of liquidity. There are no bids anymore therefore it is impossible to close any positions. Flash crashes are becoming more often and even entire exchanges (Nasdaq few days ago) get shut off.
It is nothing to do with IG or any other broker, it is just a simple operational matter.
The best you can do is to use guaranteed stops, the comission is relatively cheap compare with the disaster it can occurs in a situation like this. You just have to calculate it as a cost of business. And let's face it, trading is not getting any easier due to machines, geopolitical issues and central bank liquidity injections.
Second best is buying a binary option (or a normal option) against your position. If you get the time right you can ensure at least part of your loss for little money. But the prices of these options are not the best most of the times, so make sure you make your calculations well in advance. It might be cheaper to choose directly option 1.
I am sorry this happened to you. I hope you can recover from it.
In an earlier post I mentioned that I was stopped by another SB co. My trade was at 0934 which was the rocket panic. OP's was over an hour later, at 1050, which was a fairly quiet period. I don't understand the reason but it must be another one.