Any chance that you just had the alarm installed? Not to point fingers at all but perhaps a extra remote was coded to your alarm. Do you still have the second remote that the alarm came with or is it now "missing"m, if so start the search amongst any "friends". Was the alarm set for silent response / page only? Was there a hoodpin that they lifted the hood, disconnected the battery and then did their work? Sounds super fishy if you ask me.