New phone, different messages

I upgraded my contract and my new phone was delivered 29 October, the friendly lady who assisted me during the upgrade process advised me that if the phone is faulty and it's within a week they will come and swap out the phone and if after a week it will need to be booked in for repairs. After the first day the phone Sony Xperia Z5's battery life kept dropping to the extent that even when not used too often the battery is on 40% at 12:00 with not too much use. I phoned the call centre to query it and was advised that it's normal for smart phones even though none of my previous smart phones was that bad and the phone advertises a longer battery life. She then informed me that because it's an upgrade the phone needs to be taken in and then the upgrade cancelled and a new upgrade implemented so I will be without a phone for a few days. This directly contradicts what was said when I did the upgrade. Conflicting stories like these damage your reputation greatly and the attitude of the lady assisting me with the fault did not help.