Device not charging

I bought a cellphone on the 24/04/2015 at Pep Store Prominade. When I got home trying to charge it the cellphone didn't want to work, then i took it back they sad they will take it to repairs. I went back on the 06/05/2015 to fetch it they told me it's my fault i damaged the device whereas I never even got the chance to use it. On top of that they gave me a wrong charger, now I'm stuck with a cellphone that is not working. When on their receipt they state that a device can be returned within 7 days from celling date.