here is what FTC saysThat's good research. However, FTC Regulations are NOT binding authority in State or Federal Courts. Meaning, you need to continue your research into both statutory and common law in the State the OP lives in, and the Federal District.
Federal laws prohibit mailing unordered merchandise to consumers and then demanding payment.
If you receive merchandise that you didn’t order, you have a legal right to keep it as a free gift.
You have no legal obligation to notify the seller.
maybe state has more laws regarding it, but not sure if (and I doubt) it triumphs federal law.
I don't think they can do that legally, nor do they care.if you've already sold it, they may charge you.