In the U.S., many hospitals have some sort of patient navigator or advocate. I’m aware of at least some insurance companies even offering such services (although I can’t speak to whether they are necessarily well aligned with patient interests). See if you can request these services.

A trusted family member is always a huge help at appointments: even if it’s infeasible to go in person, ask to listen in remotely. I’ve been in those shoes too.

Be overcommunicative, be the squeaky wheel: for our part, we know the difference between even zealous advocacy (great!) from disruptive behavior (not so great!).

Sorry, the system can suck. I promise you that every oncologist has had to make those unanswered calls too, so we do know something of this end of things. But you and your loved ones don’t deserve to suffer for it, so don’t be shy.