OK so here is my solution to the network issue. I previously tried everything, from system reboots, airplane mode, network reconfigurations, factory resets, new SIM card, helpdesks, YouTube vids, and much more. Total frustration. Finally, 2 days ago, I stopped by a little one-person phone repair shop to buy a charging cable and mentioned my problem to the guy. He said he'd have a look at it and to come back in two hours. Sure enough, he found the problem... it was a faulty Antenna Flex cable. This flat cable links the main-board to a sub-board inside the phone and is a vital part of antenna functionally. The clip at one end was not connecting correctly to the sub-board. He ordered a new part and the next day he clipped it into place. All up charge including labor and tax was £60.00. This flex-cable doesn't need tools to fit it (apart from opening the back of the phone of course), it is literally a finger tip press to clip it in. Blow me down - the phone now works perfectly and has a strong signal. 
