Please feel free to write in english, if you accept baDenglish 

Bei einem bestehenden Vertrag sollte die Rufnummer bekannt sein?  Was wurde denn schon im Rahmen der Anschlussübernahme unternommen und wann?

Sorry, it appears I was mistaken about the “Check your mailbox” notification. I realize now that this was an email.

I have already executed the transfer and received the welcome email. Do I need to return the router of the previous customer or can I use this one?

Currently you don´t should send back the router. Check confirmation for router as part of the contract.

Also, if a new router needs to be sent again, how can I do that?

If you get a new router, the old router must go back!

My contract says this: 

“Bitte stellen Sie sicher, dass Ihnen der vorherige Vertragsinhaber den O2 DSL-Router ausgehändigt hat, da Sie andernfalls den Anschluss nicht nutzen können”

I have not received a new router

Hi @jrcheeseman 

Welcome to our o2 Community and welcome as a new DSL Customer. 

You have to use the router from the previous contract owner, you wont get a new one. 

If you are going to cancel the contract in the future you will have to sent back the router to our logistic department.

Dont hesitate to contact us, if there are any question left unanswered.

Best Regards.

Matze