Migration failure

Usually a great email provider, who 3 weeks ago did a "migration" that caused me to lose all my saved email folders on Outlook, caused my iPhone mail to re-download 37k emails, and the syncing of my devices to no longer work. What is shocking is that their "support" for the migration can see the problem, say they can fix it, then do nothing! Their "help" chat only responds after 2 days and each time a new person asks the same questions the previous people did. Surely, they can just email us and advise what a senior person can do (or can't do) so that we know what is going on. Best would be to just call me.