You can login your Hosting Control Panel and use the Upgrades section in order to purchase additional monthly data traffic for your website. Or you can wait till the beginning of the next month when the data traffic counters will be reset and your website will be visible online again.

You can come back and visit this website in the begining of the next month when the allocated data traffic will be reset automatically. Then this website should be working again, unless something else happen to the website and its contents.