7 Day return Policy not withheld

I bought the cellphone in pep cell store and they told me that they have a 7 day policy if the phone has got anything wrong with it . When I charge the battery of the phone couldn't last even a day without using a phone .i took the phone back the phone back to the shop then they refused to help me they told me that the 7 days is over whilst I bought the phone on Saturday I took it back on Saturday they told me that my 7 days got finish on Friday they started counting on the day I bought the phone which is amazing because a day is 24 hours according to them they counted Saturday as less than a day and my 7 days was finished. I'm not happy the way they treated me very upset with my money buying a phone that needs to be repaired and I asked for their manager wasn't there at the shop they give the number to call him and the name of him is given Khosa making me to lose more money than to save and go to buy myself another phone I'm very cross with them.