If you are currently on a prepayment meter and have a balance to pay, it is likely this is because there are outstanding charges on your account from before you switched to prepayment.
It is best to contact your energy supplier directly if you have any concerns. You may be able to add the balance to your meter and pay it off that way.
If you decide to contact your supplier please let us know by emailing email@example.com and we'll place your account on hold to give you the space to do so.
If you are worried about your energy bills you can find lots of helpful resources here.