Hello I have an 11 month old iPhone 6s Plus bought from Apple 11 months ago. It is fully up to date at IOS 11.2 etc and has suddenly stopped locating to 3G talkmobile ( Vodaphone ) signal even in strong areas. It just keeps on saying searching in the top LHS screen rather than Talkmobile 3G. Which my wife's iPhone 7 nearby, sees easily. A SIM card swap with wife's did not help and the sim was not happy in hers. A new sim was supplied and after many restarts & resets it works for a day or so before failing & goes into searching mode for the 3G signal. The new sim works in hers but only intermittently in mine. A hard reset has not cleared it. Any advice please?