can't hear a sound

i suddenly can't make any calls, as i can't hear even the ringing on the other side while i'm calling someone. also the other party can't hear me as well unless i used the loud speakers then i can hear them and they can hear me.
also suddenly, i can hear the voices but as if they r far away, i checked my ringer and sound volumes and they are at the highest.
i don't know what's the problem or how to fix it???

any help plzz