I burn old data after 7 years like tax returns and what they're based on. So I've still got a spreadsheet showing my electricity bills, readings whether estimated by them or actual ones read by me, going back to 2012.
My average units per day between bills is remarkably constant - but it goes up a little if I have guests for a while and down a little if I take a long holiday abroad in the winter months. Well I never.
I've also got copies of all my letters of complaint about electricity bills: EON 1 letter, NPOWER 4 letters, current supplier SWALEC no letters (so far) at least personally.
Don't start me on the company's electricity bills. I had 19 pages of them recently from SWALEC ranging in value from 50p up to nearly a grand for the same quarter, all estimates and they had the historic data too going back several years. As they correct one mistake they introduce more.
At my age I do know the difference between a kettle and a light bulb. Smart meters are nothing more than an indictment on the latterday teaching of physics in schools unless they mainly are for the electricity supplier's benefit.