バンフでは、そのお届け日に家に居ないとまたカルガリーまでその荷物は戻ってしまいます。　しかもお届け日はいつかは分からず、２度目のお届け日をお願いするのにカルガリーまで電話をしなくてはいけません。

自分で考えたのですが、正しい文に変えて頂きたいです。

in Banff, we usually use post office box because if we are not at home and the post office visited us to give them, they would be returned to Calgary.
we have to call the post office in Caglary and ask them to send it again but we have no idea when they will visit us to send it again.

誰かにバンフでの郵便状況の説明でしょうか？PO Boxを利用する理由でしょうか？

Most of us have a Post Office Box in Banff because if you are not home when they deliver a mail, they would take it back to Calgary and you would have to call Calgary post office to deliver it again. and they don’t even guarantee the ETA(estimate time of arrival).