I have serious signal issues at home, I cannot recive call or make calls when at home. Even when I move around around the flat I can be lucky to have one bar signal strenght, even when there is signal, calls will not come through. No matter time of the day.
I had this issue for months cannot even make a phone call.
data is terrible.
You could try wifi calling https://www.o2.co.uk/connectivity/wifi-and-4g-calling
Some help on indoor coverage here Guide: Do you have poor coverage / signal Indoors? This may help Explain / resolve it