Where can I see bandwidth usage
To view bandwidth usage of an instance login to your dashboard, then click on My servers, click on Manage -> View information for the server who's bandwidth you wanna view and it will be displayed together with other useful information such as login credentials, IP, location etc..
Please note that bandwidth overage is charged extra, in Europe and North America the overage cost is $0.02/GB, in Asia the price is $0.05/GB and in Australia, it is $0.10/GB. Your bandwidth is never reduced and only the highest value out of incoming vs outgoing traffic counts. Bandwidth overage is charged on an hourly basis and the cost is logged together with the instance itself on the billing page.
In the event of bandwidth overage, the low credit email warning is usually triggered. This gives you a hint about the overage in case you would like to take actions.