Get proof of payment agreement in writing.

"Get it in writing," says Jerry Jarzombek, a consumer attorney in Fort Worth, Texas. "If they told you half of it satisfies the obligation and that's what you want to do, have it in writing."

Send a letter to the debt collector outlining the payment agreement. You'll want to send this letter via certified mail so you'll receive a receipt once the letter is delivered. Keep a copy for your records.

If you plan to pay by check, add the following disclaimer: "Cashing this check constitutes payment in full." Write this right on the check.