Its bad news I am afraid, you can not make O2 investigate this, it is a commercial matter for them.
If someone is pretending to be O2 and they are not, it is not for O2 to investigate. This is a criminal matter and it would be fraud by false representation.
This is why the Police should investigate the matter and indeed your local Trading Standards.
But O2 is under no obligation to report someone pretending to be them - because that is what the Police are for.
I am sorry if this is not the answer you are looking for and it is certainly not the one I want to give you, but I have a duty to be honest.
Can I clarify anything for you about this today please?
If you could not make use of the service then you are paying for something you do not have. This means that they are in breach of contract and you are entitled to a refund.
If they refuse then issue proceedings in the small claims Court www.moneyclaim.gov.uk