We don't place caps on our customers accounts, it is possible to set up your own personalised usage alerts.
Log into your My Account scroll down to Details section and click on View my Bills and Recent Charges. Once in our Billing Portal, hover over Customer in the top banner on the screen, you will see a section that says Usage Alert Rules. Here you can set up alerts that will be sent to you via email about your spend or usage, more information here: Set usage alerts.
These alerts will never put a cap on your services, but at least you know when you are 75% through your data or have made £10 worth of calls allowing you to stay in control.