Can I still use my iPhone 12 after cancelling my contract?

Hello everyone please no hate. I have a phone on 02 iPhone 12. The contract is one direct debit but am charged like £11 for device and 25 for the sim I called 02 and said I’m really struggling with keeping up to date with my bills and I asked if I cancel the direct debit would the phone be blocked the person said no all would happen is I would receive a final termination fee. To be honest the phone is crusty now due to use so I have no intention of selling but just want to know if I can use it still thanks

[Re-Titled by Moderator]