Hi, this is Jim, thank you for the question - I will do my best to resolve this quickly for you.
Sorry to hear of the issue.
You can allege breach of contract against Origin (you have consumer rights here which have been infringed in my view) due to the poor service.
Given the circumstances of your case I recommend that you make a formal complaint to Origin and if that does not resolve the matter ask them for a final response letter (a "deadlock" letter). You can make the complaint here: https://www.originbroadband.com/complaints-policy
Once you have the deadlock letter the next step would be to escalate this to the Communications Ombudsman - they will investigate and liaise with Origin which would hopefully result in a cancellation of the £600 bill. They can also order the phone company to make a financial award if they have acted poorly.
The service is covered by the Consumer Rights Act 2015 so you have a right to expect a reasonable service - if they do not provide that then the regulator will step in.
You can escalate to the Ombudsman here: www.ombudsman-services.org/sectors/communications
Or by email: *****@******.***
During the complaint process they shouldn't take any enforcement action against you. If a debt collector contacts you then tell them you are going through the complaints procedure with Origin as you dispute their bill.
If they do sue, you will receive court documents (a response pack) which you must complete and return to the court. It is a tick box exercise for the most part and there is a short section to write a defence which is easy enough though please feel free to come back to this site if you need any more help. A claim will also take 6-12 months to be decided at court. If you lost then you would get 14 days to pay the judgment before the claimant can enforce the order, and 30 days to pay in full before it is registered with credit agencies. The claimant cannot recover legal costs if they win, in a claim under £10K (a small claim), all they can claim are the court fees and interest. If you were unable to pay the full sum owed at that point you can also ask the court to pay by instalments (a simple form is sent in, form N245, and a fee of £50 unless you qualify for a fee exemption so if you are on a low income, have low savings or in receipt of benefits then you would qualify).
I can assist you going forwards if it gets to the point they issue a claim.
I hope this helps and answers the question which is easy to understand - please feel free to ask me anything else. I will reply as soon as I can to help with any further queries.
Thanks for using our services and have a good day,