Bad service and lies

Today is the 7th day that I have my new Hisense E30 which is giving me trouble,I got to the counter and the manager of village mall Pep refuses to replace my phone she said that it's more than 7 days,I didn't argue and still have the phone and the slip ...and mind you this phone was in the display,what should I do as I'm very disappointed in the service and the way I was violated