You would need to ask customer services @Bullet139 but if I had to guess it is to stop excessive bills being run up.
All contact methods are in the guide below
Guide: How to find help & contact O2
And all bar information is in this one
Guide: O2 BARs
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 Do not publish personal details (email, phone number, bank account).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
