Why cannot the collectable appear???

[darkknight0453]

I wanted to go for stephen curry but the sixth man trophy just won't appear, i ve done uncountable amount of tries on award winners missions ,did 128 times on collectable exchange and 30 times on award winners exchange but i still cannot get my hands on the sixth man trophy. Is there something i am doing wrong? Is there a bug that it won't give it to you? Or is the game just being a *?! Please help me