This question already has an answer here:
Let's say you place an order for three items A, B, and C. You order quantity one of each, but get two of item B, because the company shipped from multiple warehouses (i.e., shipped two of the item by accident). You did not get charged for the extra item B, whose value is say $400.
Are you obligated to inform the company of their error and return the extra item B?
Some additional circumstancial info: We are dealing with a large internet sales company here and not a fellow Jew. Also, it is not a Jewish owned company.