when paying are you paying for the next 30 days or the pasr 30 days

Prepaid plans are always for the next 30 days (or month) - unlike some other hazy ISP definitions prepaid actually means prepaid.

If on a “post paid” account a little bit of both and the term “post paid is somewhat nebulous in terms of the actual service; the detailed bill shows the service period covered, and the bill is “issued” at the day before the start of the service period and is not due until later in that period.

For example, my last bill was issued on May 20 and is for the current period (May 21 - June 20); it was due today (June 13  but paid on June 11 using auto-pay) - so technically I paid for past service and future service. Any added charges excluding service are actually post paid. So right now, I'm paid in advance for service through June 20.

Regardless, the detail billed for post paid accounts details the period covered.