How do i change my new o2 sim card number to my previous o2 number? thankss?

would anyone b able to tel me where and how i change my new o2 sim card to my previous number, and would anyone b able to let me know if it will still take a pound or so from my credit because i lent a pound on my previous sim about 2 months back, and finally will i still get boltons as i havent topped up for 2 months thankssHow do i change my new o2 sim card number to my previous o2 number? thankss?
The only way to do this is to ask O2 to issue you a SIM card with your previous number, or a duplicate SIM if the previous one was an O2 SIM. They may wish to charge you for this but if it's a change from another provider they are limited by law as to how much they can legally charge.