PM is on a 30 days cycle and not monthly cycle. You renewal date changes every month by a day. Your account will show when your renewal date is.
Are you running out of data for this month?
It is cheaper to just buy data Add-on or use home or local wifi or use TextNow or WhatsApp app through wifi.
It is not possible to pay every month on 17th or ANY other fixed date.
PM's billing cycle is 30 days not fixed day of the month so your pay date will vary from month to month. Yes, it is possible to have 2 months bill payment on the same date, depending on how many days those months have.
Eventually, over few year your pay date will creep toward beginning of the month.