you could go on their website and create a “virtual” card (or several), complete with number, expiration date, etc. You could set it up to “self destruct” after it was used once, or a maximum had been reached, or mane even other options.

Then you could sign up for those free trial periods using this virtual card, then disable that virtual card and never have to worry about remembering to “opt out” after the free trial period had elapsed.