Q: How Do I Quit Apple Music?

If you want to cancel it simply turn off automatic subscription renewal.

You may find the instruction how to cancel it here: Manage your Apple Music membership - Apple Support

You should be able to turn-off the 'automatic renewal' in your billing settings... after the

initial trial period, your method of payment would otherwise be charged, to continue.

It is your membership that would be automatically renewed in Apple Music, otherwise.

https://www.apple.com/support/music/getstarted/

Apparently the portal to the Apple Music is within the umbrella of iTunes support:

http://www.apple.com/support/itunes/

Most of your online payment items may be presented in your iTunes account;

if not directly accessed inside Apple Music application by a link, essentially to:

https://www.apple.com/support/itunes/account/

Hopefully you can take care of this matter, you should be able to contact a Support

person from within iTunes section, per the above.

Good luck!