How long should it take for my refund to be issued, and is it ever going to be?

I was trying to purchase My First Pets for The Sims 4. From the website: "To get the pack on your Xbox One, you first need to own or purchase Cats & Dogs. For $39.99, you can get a bundle including both packs. If you already own Cats & Dogs, you’ll still add the bundle to your cart, but you will only be charged $9.99 for the My First Pet Stuff." I was not charged $9.99, I was charged the full amount. I already had Cats and Dogs, I bought it as a bundle with my game years ago. How do I get the money back? Everything is on sale right now so I payed $23ish for the bundle, each stuff pack is only $6 right now so I should get $17 back but honestly I don't care if they charge me the not sale price. I just don't want to pay the full price seeing as I already have the cats and dogs bundle. Any suggestions? I tried contacting Microsoft and they sent me here because apparently you can't contact them for refunds.

:)