7day waranty

A new phone was received before Christmas late in the evening, after i waited for a extra week because they forgot to order it in the first place. I received it late Friday evening and was just happy to get my phone. Problems occured on Christmas day with the phone decided to take it back but obviously they were close, that i understand. But they changed there closing time as they felt like making it hard for me to go after work. I had a off day on Friday so decided to take it then that to my maths is the seven day making it stil in the time frame of the 7day warranty. They ruffused to swap my phone out beause its the 8th day according to them. That is realy poor service. The person even admitted the phone has been giving this problem but nothing was mention when the phone was chosen. Thank you