If your energy company's billing is evidenced as significantly inaccurate AND you've told them in writing, then an entry warrants threat, with any second instance of a demand for payment, may become harassment, a demand for payment with menaces, and attempted fraud.

Call the police on 101, report the crime and insist on receiving a crime number for the harassment offence (otherwise you may be shunted to the utterly ineffectual Action Fraud).

A UK constabulary has now reopened its fraud investigation of Eon and Ofgem under the direction of a senior detective, having recently concluded that there had previously been police errors in understanding the law on corporate criminal prosecutions*. I suspect that the scale of the ongoing fraud across multiple energy companies may require the engagement of the Serious Fraud Office or the National Crime Agency. 

*Note: many forces are getting this wrong. I have one force making a national report pointing out that police officers don't understand the law on prosecuting corporate entities and that this needs to change.

If you have meters that have been installed for many years, use a subject access request served on the energy company for sight of your account records AND the certification for the meters. Energy companies are legally required to hold certification for any meters relied upon for billing purposes. No certificate, no bill.