I'm not a lawyer so this isn't legal advise. Its my opinion as a random person on a forum and if you take my advise without checking facts, well... I'll happily frame the summons as proof that there are indeed people that dense...
In this situation the item should be considered a gift per 39 U.S. Code § 3009 (links below, you're welcome and please read the actual law for yourself). If you were shipped the wrong item, the original item should therefore be considered unshipped. A legal contract is formed when you buy something online which bascially says that when an offer has been made by one and accepted by another, an exchange of material value called consideration makes it binding. In this case, consideration is made when the merchant charges you for items you have purchased. If they don't ship the items they are legally bound to produce, you can stop payment or dispute the charge, however you want to sound when telling the company you are taking your money back, fair and square. Among other things, a merchant might be accused of crazy things like wire fraud, fraudulent misrepresentation of material facts leading to the decision to purchase the items, RICO is a far stretch but fits the bill if involving a third party seller on a merchant, but realistically nothing of the sort will ever come unless there is widespread fraud and a bunch of people have the same complaint to the same government that really only cares when they're about to look bad (or worse).
Normally you have 60 days from the statement date of an error to report it to your credit card company or bank, but there is a second type of dispute that you can file up to a year after the purchase (or maybe the statement date, I'm not sure, so go ahead and quote me if you'd like to explain to people that you were the one who followed a stranger's advice online). Its in the fair credit and billing act or whatever that's called, i don't have the information off the top of my head since I didn't have to deal with that nonsense. The bank will give a general sigh when you bring a stack of paperwork or email an encyclopedia of evidence, but once they have it they should run with it. Don't piss them off, whatever you do, and don't tell them to work faster because you want your money. They know that you want your money and you shouldn't mess with the bank employees for the same reasons you shouldn't mess with wait staff or bartenders... They have the a great deal of influence in how smooth your business moves.
https://www.consumer.ftc.gov/articles/0181-unordered-merchandise
https://www.gpo.gov/fdsys/granule/USCODE-2011-title39/USCODE-2011-title39-partIV-chap30-sec3009