I've heard that ignoring their mail works quite good. They usually don't pursue a case once they see they actually need to work for it (e.g. really go to court). As far as I know, they will send a series of letters, each one more threatening than the last one, but most of them will not actually go to court, as there are enough people who make for more easy pickings (e.g. they pay once threatened with a lawsuit).
Plz keep in mind though that we cannot give you any real legal advice here... The only thing I can offer is hearsay.