I recently had a problem accessing O365 MS Teams. I was getting an error message saying my TLS settings were outdated. I enabled the TLS 1.0, 1.1 and 1.2 settings. I was able to download MS Teams but couldnt sign in because of an error message saying I wasn't connected to the internet even though I was. After many attempts at different solutions my IT support company worked out it was because of my internet child settings which were blocking chatrooms. If you have tried all other fixes you might want to consider this as the potential problem. They also changed my DNS server settings which also helped resolve it.
I hope this is helpful for someone.