I could be wrong but that seems very low (750 units) so 750 kWh?
Last month I used 270kw and my heatings very rarely on( like an couple of hours a day)
I live alone in a. 2 bed terraced with one shower a day
I think he’s mistaken- I’d say he’s used at least 1700
In my very poor maths surly your gas consumption is around £100
90 x 26p standing charge
750 x 10p per kWh.