they giving me excuses to replace my phone

I bought a new phone on the 8th of August,the phone had a line on the screen when I took it back to the store I was told that they will take the phone back to the supplier.when I read the phone policy it state that if the phone gives me a problem within the next 7 days I can take it back to the store and I will be provided with a new phone of which I took mine 6 days before and I was told a different story no one has called me till today I even called their head office they will get back to me of which they haven't I find the not consistent with wheir policy