Vana

The tactic is to harrass you. Hence the work phone. They probably called your mother and boss too.

Fool me once, shame on you, fool me twice, shame on me. Now you know for next time.

There could be a civil suit against you? After all, so it seems you have not paid back what you owe and promised, by signing a contract? How would you feel if someone stiffed you on a 600 quid debt? You are the one in the wrong, you do realize that? For taking the debt in the first place, for not having been responsible to have saved so as to avoid taking the debt, and then not paying it back in a timely manner. The best advice is: next time be responsible.