There is only one reason why it is not possible to cancel the subscription yourself. This is if you are in arrears and have outstanding invoices with Adobe.
In this case, you will have to go through customer service so that Adobe can explain to you how to resolve the situation. Adobe customer care can be contacted by beginning a secure chat session at https://helpx.adobe.com/contact.html?rghtup=autoOpen. Pop-up blockers need to be disabled! If the chat window fails to open, or is non-responsive, use a different device to start the interaction. Support phone numbers may be found here: https://helpx.adobe.com/contact/phone.html. Please note that phone charges may apply.