iCloud
If I buy the 50g of iCloud storage, how long will I be billed the $0.99?
Question marked as
For as long as you want to continue to use the storage; i.e., until you cancel by downgrading. See: Downgrade your iCloud storage - Apple Support
It is similar to renting physical storage space or renting an apartment; you continue to pay for as long as you use the space.