This type of situation is depressingly common in the consumer energy market.
Unfortunately, the normal laws of contract and recompense for goods and services do not quite apply in the consumer energy contracts. The energy companies have the statutory right of a “Deemed Contract” whereby they can charge an occupier for energy usage at a property even when the original consumer in whose name the contract was made has vacated the property.
While this protects the energy suppliers from their customers vacating the property and not directly terminating the contract while the gas and electricity at the property continuing to be used by the new occupier, it often causes the new occupier a great deal of expense and inconvenience as they are being charged at much higher rates and/or based on meter reading estimates which are wholly inflated by comparison to the actual amount of energy being used.
I recommend that you withhold payment on the second account and complain to the energy company that you were not occupying the property, not actually using the account, the charges are based on estimates as opposed to in-person meter readings and that you were paying for your actual energy use via your own account with the energy company.
You should attempt to negotiate a cancellation of the charges, or otherwise a reduced settlement with the energy company.
If necessary, I suggest that you instruct your own meter-reading expert to prepare a report to the energy company which can be used in Court Proceedings as an Expert Report as long as it complies with the provisions of Part 35 Civil Procedure Rules 1998.