Of course I agree they were robbed there. Considering what that Kasımpaşa player did, a penalty would have been fair. But what is fair isn't necessarily what the rules say.
I checked the "laws of the game" at the FIFA website, and they actually don't state anything about what should happen when a second ball enters the field of play. It may actually be (but don't take my word for it) that the referee did nothing wrong in letting play continue, but that the only action taken should be a yellow card for unsportsmanlike behaviour (and no penalty). Why?
Well: The second ball may be considered a foreign object like any other, rather than a ball in play. Think of the beach ball that caused Liverpool to lose 1-0 at Sunderland a few years back. Had a Liverpool player picked it up and thrown it away, it would of course be no penalty. My point? Just because the foreign object entering the field of play happens to be a ball similar to the one in play, doesn't mean it is itself a ball in play.
In other words: In order to say whether a penalty kick should have been given or not, we need to know what the rules say about a player using a foreign object to divert the ball. I've not been able to find out. Would be fun to ask a referee.