Not losing my hard-earned money over mediocre workmanship

I purchased Premio S57 cellphone at the Ackermans Moruleng mall branch a little over 2 weeks ago and was and still am extremely disappointed with the battery life. I followed the store assistant's instructions to charge the phone for 3 hours once I got home. I started using the phone after having charged it and it kept switching off on its own even at high battery levels as of day 8 after purchase. I was told I could only return the phone within 7 days and feel this is done on purpose as the makers of the phone knows how unreliable their handset is.