Whatsapp Bug - Voice is not sent outside of local network

I encountered a somehow strange problem, which leaves me in the dark. I have a Samsung S10 connected to my local WLAN. When i call my relatives - whether voice or video call - my voice and video is not send to the other person. However, when i call my other phone - also connected to the local WLAN - everything just works fine. I disconnected the phone, deleted the WLAN connection, reinstalled WhatsApp and restarted the phone, but nothing seems to work. Calling my relatives from another phone also works just as expected. Does anybody know a solution or a something i could try?