Since you were billed recently for a visit that happened more than six (6) years ago, the bill against you in the event a lawsuit is brought would be most likely time barred under the statute of limitations of your state.Ordinarily breach of contract (written) and common counts claims for services rendered have a four (4) year statute of limitations from when the debt was incurred to bring suit for payment.I would call the accounts receivables department of the medical practice that recently billed you after six (6) years to see why you are now being billed for such service or services after the passage of such a long period of time.From what you have written, I see no liability for you due to the statute of limitations bar.