Re: not sure if this is a bug.. but more of a issue

You're confusing a possibility to receive a character piece for a guarantee of a character piece.

Unfortunately the sort of random generator which they use to determine the content of Sticker Packs offers no guarantees at all and the amount of PvZ coins which you have spent or the number of times you have not, or have, received a character piece has no effect whatsoever on the content of the next Sticker Pack that you open.

The higher the rarity of the character for which you're trying to obtain pieces the lower the likelihood that you'll get a piece to it. The completely random nature of it means that some people will get the character pieces relatively quickly while other players will spend millions and millions of coins and still come up empty.