I had exactly same case. I could not use Samsung galaxy 4 anymore
Samsung company made every galaxy 4 volume control switch defective.
many people find out Samsung galaxy 4 defective volume control switch
out of order after use , it became bent right away.
because Samsung company use cheap material less than standard.
Samsung told me 1 year manufacture warranty policy before I bought and then after I bought within 1 year it became defective ,it should cover under warranty
but they sent me email not under warranty.
please watch out Samsung company from Korea and galaxy 4 .