Our rule was one sport, one musical instrument - your choice, feel free to try out several, but you will do something in music and a sport at least through mid school. We left practicing up to them for music, because life is crazy and busy and none of our kids had a passion to become a concert performer or musician.
I'd personally back off and not see pulling the plug as punishment but not paying for an extra that maybe has outworn its place in his life. Ask if he'd rather play a different instrument. We were thrilled when our kids picked band, because it took the "work" away from us and into school where it was also an escape from bad fitting academic classes.
And with our youngest who is 2E, it is a different story. He can't handle as much on his plate, so we don't push it as much. He does track and the rest of the time just goes to the gym and he plays drums in the band. When he practices and home, I tell him how nice he sounds, but I don't require practicing. His life is way too stressful to add more.
