My iPhone 4s charging case won't charge my phone?

I just got a phone case that is supposed to charge your phone. As soon as I got it, I put my phone in it. When I did that it was perfectly fine until, I charged just the case. After I charged just the case and put my phone back in it, all it does now is show that it's plugged in for about 2 seconds and then stops. This goes on repeatedly until I turn off the case. I have tried putting the phone in the case and charging both; I have tried charging just the case, I've tried just about everything out there on the internet. I'm currently contacting the seller and am trying to get a new one. Before I give up, I'm hoping for some ideas and I know my phone is not the problem.

You could probably replace the case as I personally think that the problem is with the case. Return it to the person you have bought from and see if you can get a NEW AND GOOD ONE.