Comment Dun & Bradstreet (Score 1) 341
Dun & Bradstreet got their start as a collections agency. (This is where the term "dun" and "dunning letter", for debt collector and collections notice, came from. They were persistent.)
They still do that as part of their everyday business.
Corporations live and die based on their Dun & Bradstreet rating. If there is ONE collections agency a large US/multinational corporation is NOT going to ignore, it is Dun & Bradstreet.
Give them a call.
You might want to consider sending a "final warning" letter, CC: to both US and EU branches, advising them that you will place the debt for collection if they don't pay up within 30 calendar days, before you actually sic the Duns on them.