I can only hear calls on loudspeaker

For the last few days I haven't been able to hear a dial tone or the person I'm speaking to. The phone just seems dead, I can't hear people and they can't hear me. When I change to loudspeaker or headphones all works fine. There's a small HD icon appearing under the phone number I'm calling when somebody picks up, the call timer is running and people say they can't hear anything at their end either. This HD thing wasn't there before, is it possible that HD calling was enabled by my operator but it doesn't get on with the phone? Anybody knows how to turn it off? It's not hardware issue as everything works fine with messenger or whatsapp voice calls.