Punching bad too hard !!!?

okay, so basically i bought this 100 lbs century canvas punching bag with a wall mount...i put it up everythings cool, but then i noticed...not so long after installation...just a day or two, the sand or w/e is in there has all precipitated down to the bottom, where the bottom is as hard as a rock...and the top is nearly empty...as i punch in the middle ..it bends and creates some effect that makes it kinda bounce...i went to the store....storeS...some said its definately defected some said its fine...some said beat it with a bat...i actually know all ones eventually do that and get hard...so we use a bat, but I JUST BOUGHT IT...its new =( so what do i do? is it a problem that i shud fight to return it to the store and buy a new one or should i just beat it with a bat and not do anything elses...OR...empty it all out and spread them evenly...? ...