If they make you pay for parking, but you have no way of enforcing it, then I would present them with the towing bill.....or better yet, make out your rent for $140 less and toss in the ticket to pad it up. If nothing else, it should get their attention.
If that hits a dead end, then next time you come home to a car parked in your spot, lay on the horn until it moves! For every person that comes out and complains about your horn blowing, show them your $140 ticket and offer to stop blowing your horn if a) the car moves, or b) someone pays for your ticket and gets the car moved within 30 minutes. If your lucky, someone will actually call the police, then at least they will be listening.
The question is simple....I paid for the parking spot, why can't 'I' park there ?
And I sure hope your truck is OK. I for one, don't trust tow truck drivers much.....I know too many of them.