Excerpt from this M.Y. answer:
QUESTION: What should be done if a package containing chametz arrives at one's home or business during Pesach?
DISCUSSION: One who knows - or even suspects - that the package may contain actual chametz, may not assume ownership of the package. If he can refuse to accept the package, he should do so. If he cannot, he should not bring it into his house or yard and should have specific halachic intent not to "acquire" the chametz. The package is considered "ownerless" - anyone who wants it is free to take it.
The answer mentions other options. My question proposes possible options that hasn't been mentioned.
Can one call the postal carrier an request that they pick up the package and return it? Of concern:
When one makes the product purchase, has he actually owned the items in the package, already? If so, then even before the package arrives at his home, he is already owning the chametz in the package, no? Even if he doesn't physically move the package, by the fact that he can request that the package be returned, doesn't that also imply ownership?
Another option - what if the shipper does not retrieve it during Pesach. Can he leave the package outside his home all of Pesach, and after Pesach use the chametz that was in it? Would it be considered chametz she'avar alav Hapesach? Or do we consider the fact that since he never requested the chametz to begin with voiding this prohibition for him?