Is there anyway to get a signal in a basement flat?
There's plenty of ways. It depends where the flat is, what the mobile coverage is like outside and several other variables.
If the flat has a WiFi network, then some networks/phones will let you call and text without need for a mobile signal.
Without a bit more information, then any answer is going to be vague I'm afraid!!
Connection is pretty good outside unfortunately my phone doesn't allow wi fi calls, my flat is in a city with a good coverage. It goes to either no connection or very bad when I enter.