warranty problem

I took my cell phone in for repairs at cell c , my phone didn't want to charge any more for some reason , they told me it was my battery and because the battery cant be removed they have to send it in to be fixed. my phone is still under warranty, not even a year old and the battery packed up. today they phone to tell me my warranty is canceled by the supplier because my screen has a crack on it and i have to pay over R2000 to get my phone repaired. my crack screen been there just after i got it and cant see how that will effect my battery . i think its just to get out of fixing there problem. this is my 4th Samsung and its real sad to get a response like that