My phone doesn't ring or notify for these apps: Skype, Hangouts, Duo, Signal

[AC Question]

It works for WhatsApp after few attempts.
This happens only in my mom's house when connected to wifi.
I reset the modem to factory settings, updated the firmware, disabled the firewall. Still nothing changed. On laptop, these apps respond but on mobile these apps show no sign that someone is calling.
Actually Hangouts doesn't even show I have a new message. I can only see new messages if I open the app manually.

I ran out of theories why this might be happening and need your opinion.
Devices are Nexus 4, Nexus 5, Nexus 7, two another Android devices all with latest software and OS updates.
Thank you
Nurp

 

[Nurp]

Problem solved. It was caused by the "family filter" of TTNET, which is the ISP we use in Turkey.