For a check you have to call o2 at 089787979400. If you don’t have a flatrate for your mobile phone you may also use the free phone number 08005251378. 

Please call when you are directly at the router. The sooner you report the fault, the sooner it can be fixed. Please do not hang up on the hotline yourself - after a few seconds it will continue!

Hi @az_ihsan 

welcome back 

Did you plug off the router for at least 10 minutes and start again? What happened? Maybe it was just a temporary disconnect. 

You may also try our DSL Hilfe App for assistance. If every step is done the solution is shown imediately.

Gretings and many thanks to @blablup ​​​​​​​