Iphone 4s volume buttons aren't working? - 1

Okay, so i just went to the apple store to get my phone fixed because the lock button wasnt working, so they gave me another iphone. I restored all my pictures and music and when i was testing it out to make sure everything is okay, the music volume is gone, it seems like it only works when i put my headphones on and thats when the music volume appears. Also when im in the home screen, when i press the volume buttons in the side, it wont work.plus i showed my dad and he said i was right. Is there anything i can do? Im beginning to believe that these are just refurbished iphones --- The volume limit is off, just so you know.

Added (1). @Adan it didnt work, but thanks for showing me a cool tip ^-^

Go to settings; general; accessibility; assistive touch; on… Then you can work many thing from there