They probably have few assets - the actual work is subcontraced. What options do you have in that situation?

There's a good story somewhere out there of a man who showed up with the sheriff to his local bank branch to start seizing their computer equipment to suction off, before the bank would obey the court order.

... by going back to court, and getting the court to order the police to do so.

Which is fine unless they know the system and how to play it - eg by telling the magistrate the second time around that they've made partial payment & have more coming, just need some time, etc.