Iphone 6s dropping cellular network.

Please help, I got my iphone 6s 64gb space grey yesterday, fab phone in all respects, but it seems to be dropping the cellular network, putting flight mode on and off didnt work, and when you went to search for available networks it came up with the message 'unable to load network list' the only way to restore network is to restart the phone.This is more apparaent when the phone is moving i.e like in the car.