My company has found that trying to collect by letters and phone calls is maybe 10% as efficient as confronting the debtor in person. I travel to different areas and personally help debtors to open their wallets.
People try to hide behind "validation," but when I get in their face and ask them, "what are you going to do to pay your debt," that validation bravado gives way to a sheepish, "here's the money I owe."