Cancellation of my O2 contract

Hi

I am using O2 DSL L ALL in package from 22.12.2015 onward. This month end my visa will expire and my management Decided to send me back to India for another assignment. IN online I requested for cancellation of my O2 contract by this month end (I will be flying back to India on September 30th). After initiating the cancellation request I received a message from o2 and says did I have to call "08005900050" phone number. It was German number no "English option which not available. Could you please help me this, I am having the Following documents to showcase did I am going back to my India.

1. India passport with German visa (work permit).

2. E mail communication from manger.

3. Mail communication for flight ticket booking for the return travel.

Regards,

Manith