I think it's a dead cert that the op's credit rating will have been negatively impacted.
While it can be very tempting to respond to perceived bad service from a service provider by cancelling your Direct Debit, don't do it as you'll inevitably be more negatively impacted than they will be, it won't motivate them to sort out your problem.
It'll be recorded as a default on your credit file which means that you'll either be refused or offered less favourable terms on any credit you apply for (e.g. a credit card, loan, mortgage or possibly even accommodation rental)
If you aren't happy with what O2 CS has told you, it might be best to try Resolver https://www.o2.co.uk/how-to-complain
The quickest way at the moment to get yourself a working mobile is going to be PAYG as @Anonymous suggested.
Hi @Barton, I'm sorry to see you've had so many issues with this phone since last year. I've just sent you a Private Message to get a few more details so we can check on our end if there's anything we can do to help you get this all sorted!
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