The billionaire investor said Tuesday on CNBC’s “Fast Money” that the tech giant is missing a golden opportunity if it doesn’t issue a bigger share buyback, and he intends to make sure that shareholders are represented even if the board does not want to go ahead with a bigger buyback. “I feel very strongly about this,” Icahn said. “I can’t promise you the stock will go up and I can’t promise you they will do the buyback. But I can promise you that I’m not going away until they hear a lot more from me concerning this.” Icahn said in a tweet Tuesday that he had pushed Apple CEO Tim Cook on Monday evening for a $150 billion share buyback, adding that the two would continue the discussion at another time. “Had a cordial dinner with Tim last night. We pushed hard for a 150 billion buyback. We decided to continue dialogue in about three weeks,” Icahn’s tweet said.