I'm not sure what anyone can do here? Your problems started when you moved house and it's obvious that O2 isn't the network for you. They don't guarantee 100% coverage in every area.
Have any of your phones got Wifi Calling? https://www.o2.co.uk/connectivity/wifi-and-4g-calling
If not, then the only answer is to try a few PAYG sims from other networks and see if they work.
If so, it seems you may have to change networks?
Not what you want to hear, but possibly the only solution.
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