I bought a subscription, but it was cancelled after a few days

When you first sign up for a subscription, you get 3 days of free use — this is a trial period during which you can test all of the app’s features.
If payment for the subscription renewal isn’t received once this time is up, the system automatically cancels the subscription and access to the paid features stops.
If there aren’t enough funds on your chosen payment method for automatic renewal, the free period is voided and the subscription is cancelled as soon as it ends.
Please check that you did in fact pay for the subscription after the 3-day free trial ended.
You can subscribe again at any time — just select «Subscribe» in the app. Once payment goes through, the subscription will be activated for the period you’ve chosen, depending on the plan, and all the premium content will be available again.