This picture reveals multiple reasons for the signal problems.
The signal present on the outlet inside your apartment appears to originate from the multitap connected to the GHV 30 E amplifier. This outdated amplifier is unable to pass the upstream signal from the modem. Furthermore, a return path filter (M-HPF-85) has been installed on the splitter (3DSS2), which blocks the upstream altogether. The AOP is the white outlet in the middle of the picture.
The current coax setup inside the building, behind the amplifier, is incompatible with Ziggo internet and interactive TV. Internet connectivity is currently only available behind the modem on the right of the picture (which is probably in bridge mode) or the Mikrotik router on the bottom right.
I am puzzled as to how you were able to subscribe as a customer on this address, since the AOP appears to be shared between the apartments inside the building. You should only be able to subscribe if your property contains its own AOP.