Can't hear a thing When answered a call

Basically I forgot to lock my keypad, and my phone decided to click on loads of random buttons, after that, whenever I answer any phone calls or try to call anyone I can't hear anything....its not on mute :/ and Ive noticed at the top corner of the screen there is this little headphones symbol, (I don't use headphones with this phone) and I think this is something to do with my problem . I've tried to go on setting but can't really figure out how to fix it. Little help please??

Thank you