I just ran into this issue too. In my case, Adobe begged me to try its Adobe Acrobat for free for two months. But now when I quit during the free trial, they asked me to pay cancellation fee! So the problem isn't us not reading before signing up subscription, Adobe is really doing scam now. Someone rich should really sue Adobe.
The "two months free" is not a "free trial". It is a customer retention incentive to encourage you to keep your subscription. When you accepted it, your subscription was not cancelled. Instead, two months were tacked on to the length of the subscription at no cost to you, letting you use the product for 14 months while only paying for 12.
The Subscription and Cancellation Terms page, which is linked from the sign-up/payment page, lays out the subscription terms and also tells you about the cancellation fee. Recently, Adobe has added a brief summary of this information on the sign-up page.