When you use up all of your data the data counter disappears from your overview page. Plan data resets and reappears upon renewal. Data add ons roll over every 30 days until completely used and then disappear forever.
@Demers - your plan data renews every cycle. Any promo data that would have been with an activation you made may have a data addon in either a 1 time thing (once you use it up its gone), or a recurring one (for some many months or ongoing..depending on the promo).
So, what data items are you talking about here? Do you have any screenshots of your addons at any point that you can share here?