The sound on my iPhone XS Max is temperamental

Sometimes it works perfectly, other times it’s muted, and I don’t been the slider on the left is up or down. I mean it’s NOT ON. I’ve gone to Settings, toggled the Sounds/Haptics (found it once all the way to the left), and on occasion somewhat to the left of full sound, and that sometimes works. I’ve also tried shutting the phone off, then on, resetting it, pressing the power and low volume to do a reset, updating the software; I’m frustrated beyond belief! I paid a lot for this phone and I’d like it to work properly.