It is not possible to reliably use the sound playback (music or pitch) and servos at the same time. This is because the PWM generation on the micro:bit uses a single hardware timer, so the period of all PWM generation must be the same across all pins.
One way to work around this problem is to use two micro:bits and use the radio feature to send messages between the two. Then use micro:bit A for driving the servo, and micro:bit B for generating the sound.
Another workaround would be to put the servo pins into a stable state when playing sound.
Here is an example: