I am guessing this is because of the unusual status of the replacement Airpod. Apple does not normally sell them individually so I would guess the standard return policy does not apply. If you want to learn more, you will have to contact Apple. You may need to speak with somebody senior since whoever answers may just be working with the same information you already have.
Refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you.
This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple for support and service - Apple Support For some countries look under “Other” listing at the end of each region. Not every country has telephone support.
