Mtn 7 day return policy

Can anyone please explain how does the 7 day return policy work of Mtn as I got the assurance from the call center that i can have a change on the device within 7 days but the store says otherwise and no feedback from Mtn customer service. I renew my contract and within 2 hours went back to the shop requesting another device where I was refused. What is the thruth behind the 7 days