Get all three of your full length credit reports from https://www.annualcreditreport.com
They should include the address and possibly phone number of the creditor. Start by contacting the creditor to see if this is an account that you recognize under a different name. It could also be that the credit reporting agency has assigned someone else’s account to your file by mistake. You can request that the credit reporting companies investigate and remove the account if it is not yours. If this is an account open in your name with the creditor, you will need to work with the creditor to close the account and then take steps to protect yourself from possible identity theft.