well... from what I experienced the game is set to give you what you do not want or need .

pink keys keep coming while I want cases !

( because pink cases are too fast opened by others while my pink keys number keep rising unused )

And silver / golden cases keep coming while I want keys !

( a lot of silver/ golden cases will not be opened because low silver / golden keys count your friends have )

so .... I found out something : when you get some golden or silver keys do not hurry and use them collect 5 or 6 keys and

be patient . Now when encountering the girls that gives gold or silver things the game will think that you are stuck with those keys and can't use them so the keys appearing rate will rise so much .

it worked for me try it and tell me what you found .

do not forget not go below 6 or 5 keys remaining

I attached a photo to make you see it yourselves