My office is located in a cellar. I constantly had EE poor signal; impossible to make a call or browse Internet without interruptions!
Following the advice from Julie, I ordered a 4g repeater to amplify the EE 4G signal.
A few days later I received the device.
Installing it was very simple (less than 10 min).
As soon as the device was connected, I got immediately 4 to 5 bars on my phones. From now on, I don't have EE signal issues any more. If you have the same inconveniences, have a look at their range of repeaters - I'm sure you'll find yours.