I can not get my number using pac LEB846182 how can I retain my old number

How can I retain my old number as I can not get a pac code using LEB846182,ta

To get a PAC code (Porting Authorisation Code) in the UK, simply text 'PAC' to 65075 from your current phone number. This is free and provides the code immediately, usually within one minute, to move your number to a new provider. The code is valid for 30 days