iMessage doesn't verify my number after updating to iOs10

After updating my iPhone 6s to iOS 10 yesterday, my iMessaging stopped working with my phone number. It works with my email (Apple ID), but my phone number is greyed out and the iMessage tab in "Settings" says "waiting for activation" and reports an error. Under the "Phone" in "Settings", the "My number" tab says "Unknown", it is greyed out and I can't change it. Already when I had turned on my iPhone immediately after updating, I didn't receive a text message with the activation code to start the phone, but I had to receive an automated call from Apple with the code.

I have tried literally every advice that I could find online to fix this issue: I have turned on and off my phone a number of times, I have switched the iMessage tab in "Settings" on and off, I have signed out of iMessage ID (Apple ID) and signed in again, I have reset the network settings, my time zone is set correctly, I have tried adding my own number to contacts (but nothing changed in My number tab in settings), ... I have waited for cca. 12 hours for the activation (not 24 yet though). Nothing worked.

When i tried messaging people with whom I was using iMessage before (so I already had a thread opened), the messages wouldn't even be sent as regular text messages. I would receive "text message failure" notification. I had to delete entire threads so that I could text them via regular text messages.

Can anyone suggest any other solution? I can only think of reseting my phone to factory settings, which from obvious reasons I really don't want to do. I am extremely dissapointed with the new iOS update.