I came from O2 a while back simply because everytime I used my 3G service at London Bridge overground train station ( London SE1 3QX), the service was RIDICUOLOUS slow. I would be sitting on the train and NO apps on my iPhone 7 that required data, would load, until the train physically left the station.
I put it down to the hundreds of people all at the same place, trying to use data at the same time (hence why data would then spring back to life as the train actually pulled out the station).
So I switched to EE, last year some time, which fixed the problem - I would then be sitting on the same train at the station, but my 4G connection would work, strikingly fast. AWESOME!
Fast forward to around 3 months ago up until now and is still ongoing - the SAME situation is now present with 4G data
I am sitting on the very same train, at around 5:30pm every weekday, on my iPhone 8 Plus, trying to get ANY app, which uses data, to actually load anything. Yep - the app sits there, loading and loading and loading, and just takes absolutely AGES, for so called "4G super fast data" to actually load anything. And yet again, the second the train actually leaves the station, ALL apps suddenly spring to life again. Its as if there is some invisible force, at London Bridge, stopping ALL data from working, until the trains actually leave the station, at which point, data just springs back to life.
Its ridiculous. EE is touted as the fastest network Try using data at London Bridge station and you'll soon realise, data is almsot non-existant.