general problems of the 2002 Audi A6

My check engine light is marking misfire but I have gotten a complete tune-up, changed all 6 coils on the engine changed all the spark plugs, I've done everything possible and changed everything I can that has to do with the engine all brand new and nothing has worked and its still saying misfire. . . I've googled this problem for Audi's and there were so many people complaining about the same thing. . . Also, I am having a problem with the electrical system as well one day my windows work the next it doesn't sometimes my lights will work and sometimes it doesn't, sometimes my radio will work some times it doesn't, the information on my dash sometimes doesn't light up and I can't see anything at night time, I have constantly been to the mechanics trying to figure out what's going on but we can't find the problem, I've spent so much money on this car trying to fix the problems but its really making it hard for me to keep spending money on my car and not being able to figure out what's wrong with it. This is very dangerous because if I'm driving at night time and my lights end up not working I can cause a very big accident I am very very concerned about these defects, my safety and others safety and would really appreciate if you can please investigate this problem because its happened to so many people. I also think something is wrong with the fuel system I'll put $60 in gas and two days later it'll almost mark empty I really don't understand how that is possible but if there's an answer I would really want to know. Thank you so much and I really appreciate your time.