Here is what I would do. Write to the company responsible for your area ( Scottish Power), pointing out the problem and asking for their help. Advise them that if you do not hear from them within say 30 days, that you will continue to use electricity on the basis that it is being provided free of any charges. Send recorded delivery.
If you send them pictures of the meter, with any numbers showing, that may help them.
I can't see that it is your problem. Either the builder did not register or because the meter was not used for a number of years, it has been taken off the central database.