It would depend on which of o2's systems you are on @Des640
If you are on their newer customer platform you can do it yourself.
Log in using a browser.
Click on the My o2 just under the big o2 symbol (top left).
The third column is for Billing, and under that is Spend Cap - click on that.
Follow the instructions on screen to set or edit a spend cap.
Remember you can only do this once per day.
If not you would need to get in contact with customer services.
Guide: How to find help & contact O2
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 Do not publish personal details (email, phone number, bank account).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
