Did you follow their cancellation procedures? Most hosts have a page where you have to cancel and then they will start the cancellation process. Your best bet is to contact them and keep trying. They are the only ones who can help you get your refund.
**EDIT: Cancellation & Refunds: Should you become unsatisfied with our services within the first 30 days of your account activation, VistaPages will refund your hosting fee subject to the money back guarantee terms listed in this agreement. Refunds are not available for pre-paid accounts and after the 30 days of account activation. You may however cancel your account at any time. You will need to contact customer serivce and verify information before cancellation takes place. You will be charged in full for the entire month in which you canceled your account. Accounts which have negative balances will be collections and all services will be terminated, including domain registrations. Refunds are never available for domain registrations. **
This was taken straight from VistaPages TOS. I suggest you read their TOS and see if it applies to you.