Also, what happens to your files if you forget to pay? they delete them or they keep them? I have never used this.
But then, incase you subscribe to a premium package or version of a cloud storage, it is important you understand that the package is often designed in a way that the bill will automatically be deducted from your card, but just incase you stopped using a card and forgot to add a new card on the site so they can continue billing you, I don't think that your files will be deleted, but rather, you may likely not have access to them until payments (both the outstanding ones) are all paid.
