Sorry, but I think you're out of luck as all purchases are non-refundable:

NA: https://support.na.square-enix.com/f...la=1&kid=77424

An incorrect purchase cannot be cancelled or refunded. Please be sure to review the service account and/or character you have selected in the “Review payment information” window that appears just before you complete your purchase.
EU: https://support.eu.square-enix.com/f...la=2&kid=78773

I accidentally bought an item from the Optional Items for the wrong character. Can I transfer items from one of my characters to a different character on my service account?

Unfortunately, once an item has been purchased, it is not possible to transfer the item to another character on your service account. Therefore please ensure you select the appropriate service account and character when making a purchase.
You could try contacting SE's main support (this forum is more for technical support for the game itself and mostly for players to help other players), but they'll probably tell you the same thing. You'd need to do it from additional assistance/contact us in the pages linked above for your region.

Whatever you do though, don't reactive your other subscription as the item in question cannot be traded and you'd just be wasting your money.