Purchase Subscriptions through website

I am on iOS, and I am on a family plan (not owned by me) which means that I am unable to make App Store purchases using my card, which includes subscriptions. I did subscribe through the website somehow, but am unsure how to access that information or upgrade (to ultra).

I assume that subscribing was unintentional, and maybe some leftover code from the app, but it would be nice to have a dedicated section so that people can subscribe not using whatever card is on their phone