Restaurant made me deathly ill to something I told them I was allergic to.?

I specifically told them that I was highly allergic to nuts. Comparative negligence would be on their side if I had not warned them. But, I did, and when I told them to hold the nuts on the salad, they did. But they had a special house sauce with ground up nuts in it that they still put on my sandwich. I had an awful allergic reaction, and I have written proof from them admitting their negligence. I plan on suing them for that negligence and pain and suffering. I also have medical proof of my allergies. Here's the thing. I sent the demand letter and they won't respond with their insurance information which they've told me they do have but again, still haven't sent to me. How can I get it? I posted this question before but all I got was, it's my fault for eating out at restaurants and for ordering a dish with nuts and hoping they'd hold them. I'm not going to live my life in a box away from society because of my allergy. Every restaurant prior has accommodated me and many people like me. I did everything in my power to warn them, multiple times too. What should I do?