not happy about the product i bought

I bought a cell phone within 7 days of the purchase the always reboot itself and I went to complain at the store as I was told that if there is a problem with a phone within 7 days i will be given a new phone, but i went there the lady that was helping said the phone must go for repair. How can they repair a phone which I only use for few days that i have not even pay my first instalment.

I call their head office for help and I was told to contact the area manager first and when I asked the lady to give me the telephone No of the area manager she refused she said I must go back to the store that I bought the phone and ask them to give me the the numbers, I told her that I am far from the store but to my surprise she refused to give me the numbers of the relevant area manager

My name is Ntswaki Leah Mo***eng Id No ********** 695083 and my card no is ********** ********** 87641 my cell phone no is ********** 294

Your help will be highly appreciated