A Migrations Authority Code is issued by your current ISP (internet service provider). This code is used then to authenticate the migration request from your current ISP to your new ISP and makes migration between providers much simpler and quicker. You should not cancel your account with your current ISP as it may result in broadband being cancelled on your telephone line. This would make it difficult for you to transfer your service and you would need to order broadband from scratch. Let the ISPs do it all for you. Your current provider may even try to entice you with a free upgrade to keep your business.