Truworths is a ****

I bought a phone on Sunday at Truworths Shelly centre, its now giving me problems with the battery it drains quickly. I went back to the store because im still within the 7 day period, but they refuse to exchange it they claim it will be taken for assessment. The 7 day period obviously dont count because its stating on the slip that it should be returned. I have been at the store for an hour now they refusing to exchange a faulty phone which is within the exchange time frame.