There are a number of ways to do this @Georgina85, all outlined in the guide below.
You might also want to check if your phone is unlocked so you can use a sim from another provider in it.
Guide: Cancelling Your Contract
Guide: Unlocking an O2 phone to use a different SIM card
Please note, this is not customer services and we cannot access your account. Do not publish personal details (email, phone number, bank account).
Link to our guide on how to contact them can be found here
