I think they were trying to scare you. Sound like a pair of assholes! You got no paperwork, and if your car is tax, insured and MOT'd they got no leg to stand on (for crushing anyway).
If you genuinely got a section 59, they would have had to of written you a ticket (they threatened me with it before and didn't give me a ticket, so I questioned it at a later date and didn't have one)
I wouldn't worry too much