Whoever did it, he's an a$$hole for just cutting the lock and leaving the gate open, regardless of how much right he believes to have to the land because he's had access to it for a long time, and at the very least, he owes the OP an apology and a new lock.
I stopped a man for making a right turn on a red light without stopping, once, and he explained that he'd been running that light for 45 years. I told him that if it was in my power to give him 45 years worth of tickets for it, I'd do so.
