Bear in mind that the 'phone itself may make a difference.
We both use the same network (Vodaphone via Asda) and have an old Doro "dumb" mobile and a Samsung smartphone.
The Doro only uses 3G, and gets a strong 3 bars.
The Samsung gets 1 bar on 4G, so switched it to use only 3G.
Side by side on the table, the Samsung still only shows 1, sometimes a flickering 2 bars on 3G while the Doro is happily showing a steady 3 bars.
According to the coverage map, we should have excellent coverage for both 4g and 3g, so it must be the phone itself.
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