I think ΔΕΗ are applying special reduced rates
at the moment because of COVID-19 so be careful which figures you compare. They will return to the original rates at some point.
I submitted a declaration back in March that the area of my house used on the electricity bill to calculate various council taxes was not correct and I supplied the correct figure. So far the figure has not been updated on my bill so I am waiting until that is correct before considering changes. If anybody else has made such a declaration they might consider if they want to delay until ΔΕΗ has got the correct figure before changing to a new supplier. I presume the new supplier will get all the relevant information from ΔΕΗ and I would prefer if they got the correct information.