SharePoint Online Document Library access really slow (practically froze)

It is a week that our FileShare Document Library was experiencing performance degradation, but in the last 3 day entire department coming back to IT telling that they can't work. These are the symptoms of affected users: a) Slow response in accessing document library pages; b) SharePoint online mail page of our tenant, where you can see all the frequent or site that you follow, too slow in some cases freeze; c) When people try to upload/move small documents (word, excel, PPT) even of small size 20/30 KB it take forever, you can see the progress at 0% for 10/15 minutes before get uploaded d) The O365 technical support, it is too slow on respond to such behavior, you expect something more when an entire organization can't work. Kind regards AP