I have received a letter from Scottish Power about an Ofgem investigation into them mis-selling and a compensation fund for those customers who lost money as a result.
I changed from Scottish power to another supplier about a year ago, but according to the letter I joined them during the period in question.
Apart from the fact that all such companies are just the same greedy b******s, how could I prove that I paid more with Scottish Power than if I had stayed with the same mob I was with previously? They mention providing evidence of my previous supplier and tariff; this means trying to find bills from at least three years ago - possibly four or five years.
It's not compulsory to make a claim. If it's too much trouble for you then you are no worse off than if you hadn't seen the mis-selling letter. However there will be some process for dealing with these cases as many will find it difficult to find their bills. Ask Scottish Power or Ofgem - there will be a contact address on their letter
The point is - how can I know and prove I paid Scottish Power more than if I had gone with another company? Utility company pricing seems deliberately designed to be confusing. As you say, not compulsory to make a claim and probably not worth the effort.
I have all my bills and consumption on a spreadsheet, but even for me I accept it would be a difficult job. All you should need to tell them is who you were with (and if possible what the tariff was called) before you switched to them. I agree they should have to do some of the legwork- speak to OFGEM. I think it'll be easier than you think
(Presumably you were mis-sold through misinformation on the doorstep.)