Try using your loudspeaker, if that persists, then check if other sounds i.e media are working. If you find that the media works then the issue is with your network or ear speaker. Try the diagnostic tool in the members app, confirm the issue and seek repair
Good question, I had the same problem when I was with EE and calls dropping as well. One just got brushed from them when one approach them, saying all is OK, even when things were not. Since I've left them and been with Three, they have been faultless, would recommend