These people are scum. They refuse to provide anything proving I owe them a debt, which I don't. They even filed a lawsuit a couple of years ago, then dismissed it the next day. They call from all over the country at all hours. Don't even try to talk to them.
Something else you can do. Make up a phoney business name and make a somewhat professional message for your answering machine. By law they can't call you at work. Most of them will remove that number from their calling list. I also have fun when they try calling my fax machine after they find out the only other number they have for me is work related. Can you imagine how frustrated they must be when they realize they'll always get a fax tone at that number? How would you feel if that happened to you. I hate it myself when I call a number and get the fax tone. They give up on that pretty quickly too.
You should have gotten his name, company name, address and telephone number and then told him you were filing suit against his company under the Fair Debt Collections Practices Act. Even if you don't know what it is and what it covers, they hate and fear the FDCPA. What you've got on them is their rudeness and harassment and not accepting there was no such person at your number. It could have been worth up to $1,000.00 to you. The more they get sued the sooner they'll either change their practices or go out of business, hopefully the latter.
It sounds like they weren't even contracted with any company to collect debt for them since they couldn't provide any documentation. There is a group of bottom feeders that look for old debts, often past the statute of limitations, check that out for your state, and try to collect on them. They sound like this type of bottom feeders.