Hello Ponyo,
Welcome to the community!
Have you had a chance to view the billing details of your bill? You should be able to view the details of your bill via My Account --> View & Manage Bill. From there, you should be able to Print and Save a PDF version of your bill. Alternatively, you should also be able to view the details online.
Firstly, you should note that your billing cycle usually starts a day or so after you activated your line. However, people are generally able to use their services immediately after activation. Any usage prior to your actual billing cycle start date would be prorated for the day or few days before the cycle started. That is likely the reason you received the first bill.
I think the down-payment was likely required since you did not have credit, otherwise it would have been on your first bill (ie $178 + $146). You might consider contacting customer service to verify the bill amounts. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
You should also note that for every billing cycle, you will be charged for the following month's usage as well as any additional usage (ie long-distance, overages, etc) from the previous month.
Hope this helps 😀
Cheers
