How to cancel…???
You haven’t given much information, but the following may help?
This is the appropriate Bulb page: https://help.bulb.co.uk/hc/en-us/articles/115001240731-Cancelling-your-switch-to-Bulb
Switch to another supplier which in due course means your account will be cancelled.
Have you submitted meter readings?
think the OP might be on PP as bulb don;t do fortnightly billing