Before the installation of our smart meter, our joint gas and electricity bills averaged £60-£70 in summer and £90-£100 in winter. There are two of us in the house. We have new windows and cavity wall insulation. We are both in our 70's and miserly with the use of power since the smart meter doubled our bills from an average of £67.00 to £122.00.
Scottish Power's answer to our request for an explanation was "Your previous electricity meter hasnt been recording properly. So, we set about monitoring carefully our usage. using as little as possible as a result they have just sent me an email to say we are in £495 in debit and they are increasing our monthly payment to £130.00.
@Artrose Unfortunately there's not enough information or specific details in your post to judge whether what you believe or what Scottish Power says is right. For example, were those (I assume monthly) payments of £60/£70 and £90/£100 based on actual readings or were they estimates? Your bills will say so. And all the insulation in the world won't make fuel bills cheap if the boiler is on all day making hot water for baths or a tumble drier is rumbling away.
If I were in your shoes I would challenge SP over in what way your old meters were "not recording properly" and how they've come to that conclusion. Then ask them for a breakdown of how they've come to their calculations for you paying back what they seem to think is outstanding usage.
Bear in mind according to Ofgem rules, energy companies are only supposed to 'back-bill' customers for genuine payment/metering mistakes, and then for only up to 12 months before the mistake was discovered.