So, the new fiber internet was supposed to be enabled last week. But the Fritz!box says: WAN connected, but no internet.
I then had a look with @wireshark: I'm seeing a lot of #ARP from ~2.5k fritz boxes, on #VLAN s 850 and 900. If I set these VLANs on my laptop I do get internet access. This does not look right to me.
As no support was available on Friday at 5pm anymore I left a message with my findings on our ISP's fault hotline, but haven't heard back yet.