You should send a letter to the collection agency explaining you do not owe the debt. The letter should include the account referenced during the phone calls you received. It should also include your name, address and telephone number. You could include the last four digits of your Social Security number and your year of birth so the agency can verify that you are not the consumer who owes the debt.
The Fair Debt Collection Practices Act (FDCPA) allows consumers to request in writing that a debt collector cease communicating with the consumer. It is important to note, however, that the debt collector can still file suit to collect the debt if the collector does not receive enough information from you to determine that you are not the consumer who owes the debt that is being collected.
Another option is to determine if the agency that contacted you is a member of ACA International, the Association of Credit and Collection Professionals. If the agency is an ACA International member, you can try to resolve the matter though ACA International's dispute resolution process. The ACA member directory is available at www.acainternational.org/memberdirectory and information about ACA's dispute resolution process is available at www.acainternational.org/ethics.