If you have decided for an o2 DSL Flex contract, you can cancel it in text form with a notice period of 4 weeks to the end of the month. Except for your written, signed notice, no further documents are required in this case.

If you have decided for a 2-years contract, please read the following:
How to do a cancellation due to moving abroad?

Thank you for your reply! Yes I have the 2 year contract and i have also already prepared the documents needed to close it. However i was moved to italy and the post offices here are closed in my area so was wondering if there is an email i can contact or a phone number i can call that doesnt have only a german tape playing.

However thanks because the info you provided me helped me find the return lable for the router

The free return label is for DHL Germany. I think it will not be accepted outside Germany. 

Mailboxes are locked in Italy? Why?

Luckily i left the router in germany with a friend so ill send her the label and she can mail it. They arr locked because of the coronavirus. So the government doesnt want people leaving the house for anything other than food shopping or emergencies which is why an email would be the best solution currently

Maybe a mailbox is on your way to the supermarket.