Bad timing - I think their support (here or by phone) is closed until Monday.
Either call Monday morning or try putting your postcode here to see if it’s a bigger problem than just you:
https://www.upc.ch/en/support/service-status/
You could also your neighbours if they use UPC and if it still works, or try Wi-Free if you’ve got access. Finally, if you’ve not tried already, pull and re-connect both ends of the coax cable that connects your router/modem to the wall socket.