Hi Rocky200,
If everything is off there is no way the meter should still be clocking, you’re right to raise this with E.ON. Before you do just double check everything is off, no fridges or freezers still on, appliances on standby, microwave displays etc.
There are cases where meters are crossed with other properties, hucksters theory is correct, this happens more often in flats, especially when meters are in communal spaces.
Is the meter communal?
If so when you turn everything off are there any meters that stop? Then start going again when you turn appliances back on? This is a test you can carry out yourself. And it may highlight which meter yours has been mixed up with.
If you call E.ON to discuss this, an appointment can be made for an engineer to visit you and test the meter and establish the problem. The meter should then be changed accordingly.
Brian