When you call, select German (Deutsch - I’m pretty sure it’s option 1) and then when they answer, just clearly ask if they speak English. If they don’t feel their English is up to the job they’ll transfer you to someone who can help.
Turn the box off for 10 minutes (just in case it’s overheated), and while it’s off pull out and re-connect the cabling between it and the wall socket. If it’s still not working and boots up to a red light then phone up.
If you don’t want to phone, someone from UPC will no doubt see your message above on Monday and help out.