Time for an attorney - spend the $300 - $500 and have an attorney contact them and file the court papers. Then the  negotiations will be much different.

ETA: it's not good for your case that the SD insurance oversight department sided with insurance company . . . .. . you have a big up hill battle and without a very good, very experienced insurance attorney, you could be out of luck and maybe less hassle, time, money and sleep to take your lumps and move on with life . . . . . . . . . .. .   sucks, but reality.