Hello, I want to share my experience so that you don’t make the same mistake and have to deal with the same issue. If you purchase Mullvad through the App Store (iOS), make sure to backup your account number, because if for any reason you erase or change your phone, you will lose your account (I’m not sure if uninstalling and reinstalling the app has the same effect, but it just happened to me).
A week ago, I purchased a subscription through the App Store, erased my iPhone while updating it, and now I can’t recover my account. When contacting Mullvad support, they told me to reach out to Apple for a refund, but Apple says it’s a non-refundable purchase. Then Mullvad says there’s no way to recover it, as they don’t have any information to help me with this (which is strange, but if true, I see it as a good thing for privacy reasons).
Ultimately, I believe the best option is to purchase through the website, as they do provide support in case you lose your account number.