Using debit/credit card you can only pay at first of month for resources used last one. You can’t pay in advance with debit/credit card.

Only way to do annual / half year payment is to get credits via PayPal. For example : you pay $100 via PayPal and you can use whenever you want, without thinking about can your card be charged.

Minimum payment via one transaction is $5 and maximum is $100. You can do more than one transaction if you want more than $100.

Also debit card are disabled in some regions because of fraudulent sign-ups so this could be a reason for not charged.

Learn more about billing at FAQ.