How To Request A Refund
Unity handles all refund requests. You should not contact Publishers for refunds. Go to your Order History to find the order you want to request a refund for, then press the 3 dot icon on the right to expose the Refund Request button.
Unity's policy for refunds is extremely narrow. If you made a genuine mistake such as buying two licenses on accident instead of just one, then they are usually pretty understanding of legitimate cases like this and may choose to refund one of the licenses for you. However, after you download the asset, Unity effectively sees this as outside of refund eligibility unless it contains illegal content or something bizarre is wrong such as the code being so out of date that it doesn't even compile in LTS versions.