Billing error?

[Joev1]

What is the name of your state (only U.S. law)? Virginia
A local company is trying to re-bill me for a bill paid in full due to incorrect billing after 2 years. 2 years ago I had an oral agreement with a representative of the company (who is no longer employed) for a free item with installation services being paid by me only. So in other words they will pay for the item but I pay for the cost of installation. So when I had my item installed they had $0 charges for the item + installation charges of xxx dollars...which was correct. I paid the full amount owed at that time. Now 2 years later they are trying to re-bill me for the item...saying that they have a written document saying I would pay for the item. The document is vague... it is written on an I OWE YOU from that company saying that I should pay for the item but it should have been written showing they would pickup the item cost. I did not pay any attention to the written document on my file because when I picked up my item and was billed the first time it was correct and it showed 0 for the item and the item was listed on the bill. Now they are trying to charge me for that ITEM.
Is it legal for them to re-bill me 2 years later?? I don't have a written document saying the item was suppose to be free because the written IOWEYOU is not the same as the oral agreement(so I don't have much recourse trying to dispute the written document. But I have the first bill showing the item with a zero charge.
Can they re-bill me 2 years later due to "incorrect billing" (which was really correct)????What is the name of your state (only U.S. law)?What is the name of your state (only U.S. law)? VA