Being passed from pillar to post

My dad is having some long term complications following a heart attack last year. He’s seriously struggling with the symptoms he is having but medical professionals don’t seem to be doing anything.

He goes to the GP, they sent him to the hospital. The cardiology department sent him home and say to wait for his procedure. No letters have come through to say when this might be. He calls 111, no help. He goes back to the GP, no help.

It’s like it’s not being considered urgent because it’s not immediately life threatening (though still very serious), but he is suffering so much and has no quality of life at all. What are we supposed to do here?