Reader is free. And your second sentence contradicts the third one. You very likely registered for the free trial version of Adobe Acrobat, without paying attention to what you agreed to, even though it's stated clearly that it automatically converts into a paid-subscription at the end of the trial period, unless you stop it in time. The fault is not only Adobe's here...
Anyway, if you want to ask them for a refund you can try doing so, but you'll need to contact them directly via chat or Twitter:
Chat support: https://helpx.adobe.com/contact.html?rghtup=autoOpen
(make sure pop-ups are not blocked; type "Agent" to chat with a real person, or via phone)
There's no email support.