This is what is known as zombie debt collection, and it should be illegal, and may be in your State; however to my knowledge this has not yet been addressed on a federal level.
It is called zombie debt collection because as you correctly noted after seven years the debt falls off the credit report. However, if the party trying to collect money from you can get you to pay even one dollar they have just succeeded in resetting the seven year clock, and essentially bringing this debt back from the dead to the living.
Is this ethical? NO Is it legal? Probably, I can not name a service I personally subscribe to but for a very small monthly fee (less than $20.00) I have a lawyer on retainer. I would call the legal service and have them write a letter in my/your behalf explaining the law to them and they will move on to easier prey. I hope this helps.