To view all your Billing support tickets, you first need to login to your Customer Zone
Once logged in, you can go to the customer menu and click on Support > Tickets to now open the My Support Tickets page.
To view all your new Billing support tickets or the ones awaiting your reply, you can go to the View menu on the left hand side and click either on New or Awaiting your Reply.
The fastest way to filter and view all your Billing tickets would be now to search for the word Billing in the search bar. It would search for the word Billing in departments and your subject or ticket content.