Beware...
If you end up placing an order while the DSL checker is still reporting the old cabinet number (even with the new speed), then the FTTC "build" will be done with the old cabinet and its FTTC twin. Even if you happen to now physically be connected to the new cab.
The "build" is the backend allocation process that allocates the port number, and tells the engineer what cross-connects to place in the PCP (or the RHS of an AIO). If the port is allocated in the wrong cabinet, then installation simply cannot happen.
And worse, the cab identity is picked up when the order is placed, and does not get updated if the databases change afterwards ... Once the database gets fixed, then the ISP needs to cancel the first order, and place a new one.