I was charged twice, even though I didn't want to sign up for a subscription. I confirmed the trial period, and then, before completing the trial period, they took my money.

The Opera browser is not compatible with Adobe - and a refund will take up to 14 days
To Cancel https://helpx.adobe.com/manage-account/using/cancel-subscription.html
-be sure to keep the verification email you will receive when you cancel
Go here and check your account to determine your status https://account.adobe.com
You may only get a refund if you cancel and are charged during the first 14 days of starting a trial
After 14 days the trial becomes a subscription and there is no refund
See https://helpx.adobe.com/manage-account/using/creative-cloud-subscription-terms.html