You'll need to get in touch to let us know, you can find our contact details here https://www.watkinsenergy.co.uk/index.html#contact.
We may ask you for documentation to prove the date you legally became the owner of your new home, or when your tenancy started, as this is the point when you became responsible for the heat charges.
If the moving in date we have for you isn't right we'll make sure that we correct it and recalculate your first bill.