Hello Angel Gamino,
Since the add-on was purchased inside the Minecraft Marketplace using Minecoins, this is different from a normal Microsoft Store purchase made directly with money.
Minecraft states that each store has its own refund policy. You can review the official guidance here: Request a Minecraft Refund.
Since this was an accidental Marketplace purchase, I would recommend contacting Minecraft Support and explaining what happened. Include the name of the add-on and the amount of Minecoins spent. They would be the appropriate place to have the Marketplace purchase reviewed.