Choose the right instruction
A PAC is for keeping the number when changing provider. For one line, text PAC to 65075 or request it through the official account route. A STAC, requested by texting STAC to 75075, is used when the number is not being kept. Multiple-number accounts can need another method.
Read before submitting
Inspect the response about early termination and any prepaid balance. A device obligation may be separate. An unused switching code is valid for 30 days; requesting it is not the same as completing a transfer.
Let the receiving provider act
Submit the valid code securely to the new provider and confirm the timing. Keep both SIMs available. Do not cancel the original line as an improvised first step. If it was already cancelled, ask promptly: Ofcom explains that number transfer is still possible in most cases within one month after cancellation.