There are 3 ways to cancel an O2 contract - (1) Online intimation + phone call, (2) Letter or (3) Fax [0]. Most routers (like Fritzbox) come with a fax function

There are 3 ways to cancel an O2 contract - (1) Online intimation + phone call, (2) Letter or (3) Fax [0]. Most routers (like Fritzbox) come with a fax function which you send an online fax [1]. O2 charges a maximum of 0.14 cents per fax page or free based on your DSL plan. Alternatively, you can also send a physical letter online (0.70 cents) [2]. Your comment below says that there is no receipt for confirmation. O2 provides a default PDF form on their website which to fill for termination. The letter explicitly states that "o2 should send you a written confirmation of cancellation". It is illegal for O2 to be in receipt of a letter and not send a confirmation. I am sorry if that happened to you! Don't get me wrong - the auto-renewal of contract practices in Germany are predatory for the consumers. Recently, there has been a change in law that forces providers to extend contracts by 1 month instead of 1 or 2 years. [0] https://www.o2online.de/service/kuendigung/ https://www.o2online.de/service/kuendigung/ [1] https://en.avm.de/service/knowledge-base/dok/FRITZ-Box-7490/193_Configuring-the-integrated-fax-function-in-the-FRITZ-Box/ https://en.avm.de/service/knowledge-base/dok/FRITZ-Box-7490/... [2] https://www.deutschepost.de/de/e/epost.html https://www.deutschepost.de/de/e/epost.html [3] https://static2.o9.de/resource/blob/498264/12cd6ca6ee17a02b9e4045de0c3d9dd1/o2-faxvorlage-kuendigung-mobilfunkvertrag-pdf-download-data.pdf https://static2.o9.de/resource/blob/498264/12cd6ca6ee17a02b9...