Welcome to the Community, dabisaleh
Since we are a “customers helping customers” forum, we have no access to network backend systems. The Sunrise team is currently not active in the forum due to holidays. Another reason for the issue could be a roaming block on your account. You can try to log into the Sunrise Cockpit (Sunrise Cockpit) via Wi-Fi to check your settings and active blocks. For an immediate check or escalation, you can try the live chat or call the international support hotline (+41 58 777 01 01) directly from another working device if it is urgent. Note, however, that this call will incur costs.
The issue might relate to local network changes. You can check your device settings to see if switching the network mode manually to 4G helps, as local 3G networks are being phased out. It is also worth verifying that VoLTE is active for roaming on your device.
Cheerio cosmo