Duplicate cards

having sames cards even though i didnt have every cards in each expansions.

I believe that, there was a 17.0 patch that there will be no duplicate cards before users have every cards in each expansion, but I have many of more than 3 duplicate cards after I opened all the expansion card packs.

Duplicate protection works in each rarity not in every card of the set. You will not get a third copy of each common, until you have all the commons, once you do, you will start receiving extra copies of commons, regardless of how many rares epics or legendaries you are missing. The same is true for all rarities.
Also, the drop rate of packs do not change, you are still only guaranteed only a rare, no matter how much of the collection you are missing. Meaning you will not start to get more epics and legendaries only because those are the cards you are missing.

yes I already received more than same 6cards, before I have all commons…

I’m not sure what you mean by “each expansion”. Each card pack is from a specific expansion (or the base set), so of course it can only give you cards from that expansion.

Surely you weren’t expecting to get Rastakhan’s Rumble cards from a Rise of Shadows pack, just because you already own all the Rise of Shadows commons?