Hello Marek,Thank you for reaching out to Microsoft Q&A and informed us about the issue. I understand that you've been trying to contact Xbox Support but to no avail, and you've also clear browser cached, this must be very frustrating, but here's some workaround you can follow:
- Use incognito mode/others browser: please try to access Xbox support using incognito/private tab on your browser or you can try it on your mobile phone's browser
- Disable any active VPN
- Try using another network, if you can access other Ethernet/Wi-fi please try switch to it or if you have hotspot on your mobile data plan, that's worth a try
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