Before you pay a dollar to a debt collector or even acknowledge that a debt is yours, call in the help of an old friend: snail mail.

Errors in debt collection are common. You don’t want to pay something you don’t owe or accidentally revive a so-called zombie debt, which is an old debt that might be past the statute of limitations. And you don’t want to fall victim to a debt collection scam.

You have two tools you can use to avoid making an expensive mistake:

Collectors are required by Fair Debt Collection Practices Act to send you a written debt validation notice with information about the debt they’re trying to collect. It must be sent within five days of first contact.

The debt validation letter includes:

If you don’t receive a validation notice within 10 days of first contact, request one from the debt collector the next time you’re contacted. Ask for the debt collector’s mailing address at this time as well, in case you decide to request a debt verification letter.

The validation letter might leave you with more questions than answers about why you owe the amount listed or whether you owe the debt at all.

In that case — or if you never received a validation notice — you can request a verification letter proving this debt is actually yours. Among the many things you can ask for information about, a debt verification letter can:

If you send the letter within 30 days of first contact, the debt collector must stop trying to collect payment until it verifies that the debt is yours. You can still send a verification letter after the 30-day mark, but the debt will be assumed valid and the collector can continue to seek payment while it responds to your letter.

It’s a violation of the collection practices act for a debt collector to refuse to send a validation notice or fail to respond to your verification letter. If you encounter such behavior, you may want to file a complaint with the Consumer Financial Protection Bureau.

The CFPB has sample letters that you can use. The key is to be thorough in your request for debt verification.

In your letter, ask for details on:

You may want to send this letter by certified mail and request return receipt so you can document the correspondence between you and the debt collector.

Be aware that although you can ask for many details, debt collectors are only required to provide information on the original creditor, the balanced owed and the name of the person who owes the debt before resuming collection efforts.

Getting even that amount of information, however, can help you determine if you actually owe this debt, if it’s past the statute of limitations, or if there’s an error such as overstatement of the amount owed.

Once you have information on the debt, how you proceed depends on whether you actually owe it and whether you’re in a position to pay the debt if you do.

If the debt is yours, you have a few ways to pay off a debt in collections. If you can’t afford to pay it, you may want to look into debt relief.

If the debt is not yours, write a letter to the debt collection company disputing the debt. You should also check your free credit score to see if the erroneous debt is marked there. If so, you’ll want to dispute that with the credit agencies.

Sean Pyles is a staff writer at NerdWallet, a personal finance website. Email: spyles@nerdwallet.com. Twitter: @SeanLoranPyles.

The article Avoid an Expensive Mistake: Validate Debt Before You Pay a Collector originally appeared on NerdWallet.