Who are you migrating from?
What does the order tracker say in MyBT? If it says something like "appointment no longer required" it probably means your current ISP has placed a cease on the line, which prevents BT/Openreach from scheduling a proper FTTC appointment until that ceased date has elapsed. (This was the issue I had).
Just a thought, did you have your home phone available when you were supposed to have the engineer round? Because when I had mine done they phoned once and I missed the call. They then called again to confirm I was actually in before coming round. It does say that in your preperation emails, that you should have your phone line available, might not be the case but worth considering.