If it has been more than five years since your last payment you are outside the statute of limitations in Virginia and the debt is time-barred. This could change if you have made any statements to the company about negotiating on the debt so be careful what you say on the phone. If you don't believe you owe anything, send the collector a letter stating that the debt is time-barred and that you don't want to be contacted again. This will stop them from doing so (legally anyway) and they will only have recourse to taking legal action, in which case your statute of limitations defense will protect you.
State laws called Statute of Limitation determines how long a creditor has to sue you for a debt & these laws vary widely between the states. I suggest looking at these laws directly as most states post all their laws on the state website or at a local law school. Hope this perspective helps!