@MikaelaYou can add a spend cap of zero to your account by going into o2.
You can find full details of what and more importantly what isnt covered here:
https://www.o2.co.uk/help/account-and-billing/spend-capYou will need to call Customer Services on 202 to block bill to mobile and premium rate calls etc
- Xperia 1V - o2 and Spusu
- Pixel 8 Pro - o2 and Vodafone UK