Alarms are a pain, might be best to get a specialist to remove it.
Chances are though that its the door lock that's the problem, not the alarm. Quite common, and worth checking out. One way to test (although its not a sure-fire way of telling).. sit in the car with all the doors unlocked. Press the button on the drivers fingerplate to lock all the doors. If the pin goes down then pops back up then its your lock mechanism that's goosed.