We have an expression for debt that keeps coming back to life: "zombie debt"!
If it still shows on one or more of your credit reports, and it is more than 7 years since the date of last activity (and there is no judgment against you), the account is “obsolete” and you should dispute it with the credit bureau that is reporting it. They have 30 days to either verify it with the party reporting it, or delete it.
If they do neither, that is when you may need a lawyer, to sue them for violation of the Fair Credit Reporting Act (FCRA). You do not need a lawyer to dispute it initially. Again, disputes should be directed to the credit bureau(s) that is reporting it (not the collector), via certified mail, return receipt requested.
However, it is not illegal for collectors to send you letters offering to settle the account, or asking you to pay. It is illegal for them to threaten you with a lawsuit once the statute of limitations has expired, but you did not indicate that they are doing that.
If you want the letters to stop, send them a letter and tell them to cease communication with you. They are allowed to send you one more letter after that, to tell you that they are stopping and to tell you what if anything that they intend to do next.
More than likely, they will then stop contacting you, but they may (likely will) send the account to a new collector who will go through the same process. You will have to send another cease communication letter to them to get them to stop. There is nothing illegal about this process. So long as each collector stops when you tell them to stop, and they don’t threaten you with suit or otherwise harass, abuse or oppress you, they can ask you to pay indefinitely.
For more information, check out the FTC’s free information at http://www.consumer.ftc.gov/articles/0149-debt-collection . If you need more help, call our office and make an appointment.