Defect PR20 LIte within 7 days ?

Took out a brand new P20 LIte on 17th January , took it home a day later the phone rebooted itself, then over week end it did it every day twice a day, I took it back to Cell U city Cavendish and was advised that they cannot give me a new one it has to be sent away for assessment? now i have to be without a phone as and a few days, I feel within 7 days i have aright to cancel this deal and get a new phone? I don't want this model if this is a problem phone?