There's a large percentage of "no longer valid" debt collection going on these days. The probability of whether a call is valid or not is probably in opposite proportion to how agressively they try to collect it. Here's some giveaways your call is probably fraud, or a mistake, or even just some ancient, no longer legally valid debt that may or may not have been yours... Or worse, it may not be anything that is or ever was valid, and in fact, may be nothing other than fraud.
1. NEVER agree to anything over the phone.
2. Ask for the name of the company calling you.
3. Ask for the name of the person who is on the phone.
4. Ask for the "address of service" of the company on the phone.
5. Tell them that as a courtesy to them, you'll accept their call to get them to send you the proof of debt - this means the ORIGINAL debt, be it an invoice, contract, or other PROOF you owe. Insist that until you see them and accept it is legal, that they take no action and that until then, you deny it all.
6. Never give your full name, address, bank account, credit card, or ANY other useful information. If they don't have it, you don't owe them any money. Even if they do have it, do nothing and say nothing, until they send you proof.
7. If they make it sound like the person on the other end is an attorney, but is calling over a matter of a few hundred or even a couple thousand dollars, tell them you don't do business over the phone and hang up.
8. Never agree to any terms of payment, or even agree you are the person who owes the debt over the phone, until or unless they provide you with LEGAL proof (which is not a summary of money owed, but the ORIGINAL source of obligation). This can't be done UNTIL they mail you actual copies of indebtedness. If they're dumb and send you the original contract, burn it and laugh. Only the original is a valid debt.
9. If the person on the other end is rude, angry, intimidating, or tells you that this is "the last chance before we take action", then kindly explain you're not interested in talking to them and hang up. Especially if this is something you know nothing about, or is very old, or if ANYTHING about it seems fishy or not quite right.
Yes, there are professional and legitimate debt collectors, but the rest have made a horrible name for the industry among consumers, who have been scammed, burned, lied to, defrauded, and in other ways abused.