If the debt is over 7years old, they cannot collect on it and cannot report it to your credit file. Fair Debt Collection laws prohibit them from doing anything to you. Reply to them and say it's over 7 years old. This link may help. https://www.consumer.ftc.gov/articles/0149-debt-collection
They are calling me on a cell number that I have only had for about three years. I that time I have had no debts referred to a collection agency. When i answer the call, they ask for someone that I have never heard of. I even tried calling them back from a pay phone to tell them to leave me alone. That didn't work either. It's just a stupid machine dialer. Don't answer and it will eventually drop your number from the list.