I have discovered a neat little hack for topping up you mobile on pay and go. Most companies use a fixed menu system. If your phone allows you to store phone numbers including hashes and pauses, you can create a contact that navigates the menu system like a robot rat. Here is the phone number you use on 02 to top up by £15;

44 44 ,#,1,#,1,#,#,9876#,543#,15#

You’ll need to swap ‘9876’ with the last digits of your debit card, and ‘543’ with the security code on the back. 

If that’s a useful trick and you use another mobile provider or phone, feel free to post your own patterns in the comments.