Why did I get billed I haven't used Yousician for a while
To ensure an uninterrupted experience for our premium users, all our plans are auto-renewing if not cancelled in time. The cancellation has to happen before the end of the paid subscription time, which is similar to e.g. Netflix, Spotify and similar subscription services. This is also clearly stated during subscription on the subscription page, Terms of the Service, and billing details.
If I get the yearly plan, will I get billed monthly or pay the whole amount in advance.
All the plans are billed once every billing cycle. So yearly premium plan is paid once a year.