This forum is for FormsCentral but I can answer your question - sign into this page using the same Email (AdobeID) as your ExportPDF subscription to manage your subscription and turn off auto-renewal: https://www.adobe.com/account/my-products-services.html#MyServicesHeader
I’ve tried many times to turn off auto- renewal through the link you provided, but I am not able to change the renewal status. Please help to check.
I can't do anything myself but I have forwarded to a Support team that would handle this type of request for FormsCentral, I believe that they will forward to the right support team or take care of it directly. Someone should get in touch with you to confirm.