iphone 4 randomly started overheating battery has died will no longer charge what do i do

Iphone 4 randomly started overheating and battery has died and will no longer charge, what do i do?
location: apple.com - date: April 4, 2013
I have had a iphone 4 for a number of months but a few days ago i was using my girlfriends charger and noticed it go extrmemly hot. it carried on today and has died and wont charge on any of the extensions i have used even docking system. I have no idea what to do, if anyone could let me know ASAP then that'd help me alot as visiting an Apple store is hard for me at the moment!
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