Here are some suggestions and I am sure these'll work for you:
Close everything, clear your browser's history, restart your computer, and log back into QuickBooks Online to see if the migration moved. If it's still stuck, check your internet connection and make sure it's strong.
If it's still stuck at 45%, call QuickBooks Support again. Get a ticket number, tell them it's been stuck for many hours, and ask them to check the actual migration progress, not just say it's working. If they can't help, ask to talk to a supervisor. Write down everything you do and who you talk to.
