Pay for bills

It is said by the letter. I only used £26.23 for my bills.but why I need to pay £45?

See: https://help.bulb.co.uk/hc/en-us/articles/115003405632-How-do-Bulb-payments-and-statements-work-

Hi @xinyue did you still need help regarding this or is the article @Hooloovoo posted a sufficient explanation?