回复：大家显示在485收据单上的ASC code是几位数?

is the ASC where you are assigned to do FP.
If you are scheduled, why do you need to make appointment by yourself.
My guess (of what you say about the immigration service person on the phone) is that they don't want to accept re-schedule of your FP appointment, if you want to reschedule, you go to the ASC in Birmingham (probably operated by a private contractor so they are willing to get your business.)