What iOS version?
Are you using an authentic Apple certified charger and cable?
What happened right before it stopped charging?
How long have you had it?
Has it been dropped ever?
Has it been exposed to moisture ever?
Have you tried a hard reset?
Long story short, your going to probably have to get it replaced if you've tried multiple chargers.
If you have any kind of physical damage on the phone you cannot get it replaced for free through warrenty. Your warrenty is standard for one year and depending if you have insurance you may also have extended warrenty if your outside the first year.
If your phone is damaged then your going to have to go through insurance if you have it. The deductible is 169.00 for the iphone.
Other option, alternate upgrade from another line, buying off ebay/amazon/full retail or they have the DPP which takes full retail into 12 monthly payments added on the bill.