Legal Question in Consumer Law in South Carolina

Re: never received invoice

They can send you an invoice, certainly, but they only have a limited time to file suit and be entitled to payment. (And they are entitled to payment - you have the benefit of the product, and they're entitled to compensation for it.) Depending on the nature of the purchase, the statute of limitations on a contract claim can vary but is generally three years. If you want to take advantage of that, it's three years since purchase, or payment of any amount towards the debt, or your acknowledgment that you owe the debt, whichever is most recent.

Or you could just pay the invoice.