What you see that input string are Unicode escape sequences. So you have to un-escape them. Since we're dealing with byte arrays though and not wide characters (double byte arrays) we then convert them to ascii after the un-escaping to get the final result in a byte array. So, try something like this...
static void Main(string[] args)
{
var encodedString = "~\0\u0015?\0\u0013?\0AT??\\?\u0001#12#12#R#\v";
var ascii = Encoding.ASCII;
var unicode = Encoding.Unicode;
byte[] unicodeBytes = unicode.GetBytes(encodedString);
byte[] asciiBytes = Encoding.Convert(unicode, ascii, unicodeBytes);
Console.WriteLine(BitConverter.ToString(asciiBytes));
Console.ReadLine();
}