That does sound unusual. If you activated your lines on the 11th, the billing cycle would have likely been assigned to be from the 17th to the 16th of the month with the first bill having a partial billing cycle charges from the 11th to the 16th. At least that's how my billing cycle is since I also started my current account on the 11th of the month many years ago.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.