Hi -- It's the power supply companies responsibility to know exactly what meters they have installed at a property, inspect them for safety and read them on time, not yours. !
I am sure when the truth is known and if they try to wrongly bill you contrary to existing agreements, that Energywatch would take up your case if you referred the complaint to them.
In accordance with the ground rules on this matter, I am sure they would find the case in your favour and only expect you to have the liability within those rules.
You may find it useful to print off that article and keep it as a reference for any future problems, it's always nice to be able to produce documents that back up what you are saying. !!