Are you sure the drop caused that issue? I see no damage on the outside of the phone--unless that damage is on another part of the device and is not pictured. I would have taken the iPhone into an Apple store (or sent it in) and let *them* diagnose the issue and the likely cause -- rather than immediately saying it was caused by a drop and therefore setting yourself up for an expensive repair from the get go.
They may have determined that the problem is not related to a drop at all and exchanged it out for free.
Just go to an apple store if you have one near you.
Obviously dont tell them you dropped it.
Just show them what the problem is and play dumb. You dont know why its doing it etc....