How do I cancel an Apple Music Voice trial?

See instructions in If you want to cancel a subscription from Apple - Apple Support

Apparently you don't know what Apple is doing now. You ask Siri to play an artist, and their new Apple Voice 7 day trial starts automatically without permission. It can't be cancelled and when it's done you will lose the ability to ask Siri to play an artist from your music library. Siri will say what you ask and then play unrelated random song.

I am concerned about the same thing. I got an email that my free trial started, without me asking for it. Apple Support claimed that could not happen with my two factor authentication, but it did. I had to change my password and set my appleID to always ask for my password when making purchases (although I thought I had already activated that setting). Apple Support brushed all of this off by saying that it’ll cancel automatically in 6 days without charging me. But I remained concerned about Apple’s profound security lapse regarding my account. This is not a “no harm no foul” issue.

I called Apple support, spoke to a senior advisor and he insisted that a trial could not have started without my request and that nobody else has complained about this problem. (I told him that there is a discussion thread already online and he offered to file a complaint for me). The only reason I even found out that my id had a free trial subscription is because I tried to redeem a 4 month free trial that I received for purchasing a new iPad. Unfortunately, I am now ineligible because for the 4 month promotion because of his free 7 day trial that I never initiated. It is so deceptive, creepy, and frustrating.

Yes it does. Free trials are cancelled the same way as a paid subscription. You may want to wait a day and try those instructions again.

If necessary, also see the "Can’t find the subscription that you want to cancel?" and the "Contact Apple Support" sections of that same support article.