cannot get on the server "The server is not responding"

[Erigion81]

Hi there,
I´am from Germany and my provider 1&1 Telecom announced 50k DSL instead of 6k. After the conversion from 6k to 50k and a new wlanrouter (FritzBox 7560) i get the same msg after character selection "The server is not responding". After ca. 5min i get back to the login screen.
I tried a few port settings but with the same issue
I realy need some help and look forward someone have the same problem and a solution at hand
Thanks folks and greetings, Erigion