i just got a new charger ordered online from the apple store app

sometimes the charger will work but other times it won't. i really don't want to have to buy a new one because the charger came with the standard one year warranty but i don't know how to go about getting a new charger for free from apple and i don't want my problem to go unheard. its a 2 meter lighting usb cable and i've tried multiple outlets in my house as well as getting a new adapter but nothing seems to work. please help.