Sandy make your approach more legal. This debt has way passed its
statute of limitation (SOL). This means that no creditor or collection agency can force you to pay the said debt and cannot take any legal actions against you.
Make sure that you do not make any payment towards this account or sign any promissory note. Otherwise, the SOL will be set from the beginning.
You can now place the dispute on two different reasons. Ask them to validate the debt if it is your bill with all the details. Later, if they manage to give you any information, you can dispute with the expiry of the SOL.
Do your correspondences in writing with the company. It is very important for you to keep everything documented in a file so that you can prove the facts at a later stage. Send your mails through certified mail with return receipt requested. You will be sure about them receiving your mail.