I had the exact same issue. Same messages on the screen, had WiFi but no internet connection, apps that require data didn’t work, etc. I was on/off with Onstar a few days. They had finally escalated my issue to a higher level of tech support. It was getting late in the evening & I told them I was done hanging on the line with them. They said they were going to continue to look into it & they would call me the next day to further troubleshoot the problem. By midday the following day, my problem was gone & they never called me back. Haven’t had an issue since.