Hello 501081174,
Welcome to the community!
With post-paid services monthly charges are for the upcoming month (see definitions here). I understand that might seem counter-intuitive since post usually refers to after. I think the term might refer to receiving a monthly bill stating any accumulated additional charges during the month (see here). While the plan fee is charged prior to each month, overages and additional charges show after each month.
For any given billing cycle, you are charged the upcoming monthly fees as well as any overages you might have incurred during your previous month. So you are charged in advance for your monthly plan plus any usage above your allotments in the previous month. Since most billing cycles start within a few days after activation, first bills usually include the upcoming monthly fees as well as prorated charges for the few days before your billing cycle started.
You should note that this forum is community-driven and not intended as a venue for customer services. We do not have access to customers' accounts. If you would like to discuss your bill, you would need to contact customer service. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Hope this helps 😀
Cheers
