You didn't reply because you had nothing. There was no lie in my similar example of bank overpayment.
The lie is that it is similar. I will take this last moment, even though I said I wouldn't, in the interest of a final attempt to make the world a better place. There is simply no congruence between a bank error and someone putting something in a box and sending it to you, and it arriving on your doorstep — obligating you to do something about it. By suggesting that it is the recipient's problem when someone sends them something unsolicited, you are advocating slavery. You may subject anyone to obligation simply by sending them something. Granted, it is a tiny little piece of servitude, but the duration does not alter the degree to which it is true. The postal service is meant to work for The People, not the other way around.
It is simply unreasonable to place the burden upon the recipient. If you cannot avoid addressing the wrong thing and putting it in the mail and sending it to someone, you probably should not be in business. If you cannot manage to provide return shipping information in such a case, you definitely deserve to take a loss on the goods which you incompetently sent out, forcing someone else to spend their time (which they will never get back) dealing with your mistake. In fact, you should be obligated to pay them for their time if you want the goods returned, since your error has caused them actual damages — time and effort lost. And in this particular example, also the delay of arrival of goods which were promised and paid for.
Most of these issues do not exist at all in the case of a bank error, which is also completely different because you are expected to track your own bank balance. You are not expected to fill the shipping crate at the internet retailer from whom you make purchases. There is simply no congruence whatsoever between the two situations, and your insistence that there is proves that you're suffering from cognitive dissonance. You think you're smart, and that smart people are right, and therefore you can't be wrong. Well, you can be smart and wrong.