You can also lodge a formal complaint, but admin will be unable to help if you do, so wait and see if they respond.
https://www.o2.co.uk/how-to-complain Take a look at the Resolver link within the link if you have to go that route.
Thanks for the mention on this one @Bambino!
@JMGrice I'm sorry to hear about the difficulties you've had cancelling this account. I'm happy to pick this up and escalate it to the credit referrals team. I'll need some details to proceed so I'll send you a private message.
→ COVID-19 support - Help and support from O2 during the lockdown
→ Access for You: Registration - Find out how to register for our Access for You service.
→ Just joined the community or thinking of registering? Check out this handy starter guide!
→ Have a query about your account? login to My O2 for help
If you'd like to take part, why not register?