There is a template for you to fill in and you can send the form by FAX or letter post.

To download. Click on the link here

Here is the translation of the letter from the German version that you will see when clicking on the link

I hereby terminate my mobile phone contract with the phone number …….        to the next possible 
Date. Please send me a confirmation of this termination, stating the termination date.

Nachname ( First Name)
Vorname   ( Last name)
Geburtsdatum ( Birthdate )
Straße/Hausnummer (Your Address and House Number)
Postleitzahl/Ort (Postleitzahl Postcode )   (Ort Place where you live )
E-Mail-Adresse (Email address)
Ort/Datum   (Place where you live and the date )
Unterschrift ( Signature )

Thank You. When I called the customer care, they told me that It is possible to take the number with me after the contract termination. It is possible for 90 days. They also told me that I dont have to fill any forms for that. Is that true?

Hello @Basilpt, it is a pity that you leave us.

But yes, that is correct. You just have to tell it the new provider, that you bring your own number.

Kind regards, Ines.