Login, use the deletion link and off you go.
URLS:
http://www.t-online.de
https://kundencenter.telekom.de/kundencenter/registriert/dienste-abos/ngcs/deregistrierung/index.html
Please note that AccountKiller.com is not associated with the business listed on this page. AccountKiller provides easy-to-understand instructions and guides on how to cancel charges and relationships from the list of businesses on our site, we have no affiliation with these businesses.
Toll free customer helpline phone number is__ +1 *866 *940 *0005 *
Call them for technical help