Apple ID is Invalid!!!!

I used to download songs and games from my apple ID. but now it shows that email address or passwaord is incorrect. I beleive that sometimes i forget my password. but there is an option called "forgot password" to reset!!!!!! . Then why i caould not change the password. And now it says your email address is not an Apple ID???!!!!. This is really irritating. Recently i bought iphone 6s Plus. and i tried to purchase and download stuff from App.store. but it always shows by email address (same email address). I open many games under my game center email address. It always says logggin. Then why it shows......if ID is not valid.

I need a solution for this urgently because i'm sick and tired of looking for the solution.

Thank you

Endheri80