The trial is the refund policy working in advance: seven days of the whole app, and cancelling inside them means the card is never charged at all.
If a charge has already gone through — a cancellation you meant to make, a double charge, anything that looks wrong — email hello@vikingur.app from the address you signed up with and say what happened. A person reads it and it is handled case by case. Refunds themselves are processed by Paddle, the merchant of record. Nothing here limits your statutory rights.