@Attariyah
Data provisions from the plan refresh each billing cycle. Anything you don't consume is lost, even though you already (pre)paid for it.
Data provisions from promo bonus/bonuses (if any) are variable, I think. Any conditions, restrictions, limits, and options attached to them would be specified in the announcement thread which advertised the specific promo.
Data provisions from add-ons (including free/gift add-ons, if any) rollover across billing cycles indefinitely. The unused portions remain available until they're used. The add-ons fall off the account once they're fully consumed.
Plan data is always used first. Then promo data, when no more data available from plan. Then add-on data, when no more data is available from plan or promo.
You will receive free text notifications when you reach 75% and 95% thresholds on plan data.
Unfortunately, the notifications don't seem to work properly if you have more data available on promo and/or add-ons. Unless they've recently fixed this issue.
If/when you have no more data available anywhere then your data connection will halt. No more data until/unless you (or your AutoPay) buy more data. Your browser will be forcibly redirected (by the network, not by your phone) to Public Mobile's "Why don't I have data?" FAQ page every time you try to go online, there's no way to sneak any data usage around it.
It's worth noting that Public Mobile doesn't have any sort of "unlimited" "endless" "infinite" data (at throttled speeds) like many other providers. You can't slow sip more data out of the straw once your cup is empty.
You can always confirm how it works by leaving a little data available at the end of your billing cycle - see whether or not it simply vanishes when your plan renews. A small one-time waste might save you from much uncertainty and confusion moving forward over subsequent months.
