Energy prices in an all electric 2 bedroom flat

I moved into my housing association 2 bedroom all electric flat with another adult in July 2018 and ever since we have had huge energy bills. The flat is heated by an exhaust air source heat pump system with underfloor heating and has 2 adults living in a 66m2 2 bedroom flat that’s all electric. I can’t seem to find out what I should expect our energy bills to be as I’m just getting information on flats with both gas and electric. When I viewed the flat the housing officer said it was only built in 2014 to high energy standards and gave me a copy of the Energy Performance Certificate which rated everything as a B with an overall rating of B. It’s all electric and heated by an exhaust air pump system. My 1st bill that had any winter period on it was from mid October 2018 to mid January 2019. I was in hospital and the flat was empty but the heating was left on low to avoid burst pipes and the bill was £529 just for those 3 months. The Energy Performance Certificate that the housing association gave me rating was a B and it stated that my energy bills over the next 3 years would be less than £1500 plus appliance usage. I would say we are low energy users. After complaining to the housing association in February 2019 I have seen many different contractors from many different companies and it took until around May last year when a contractor said my bills were so high because the heating system was too small and the housing association put a different make larger system in 3 months ago but the bills are still huge. Just for December 2022 we used 1067kwh just for that month. How many kWh should we be using? Please help me out because I’m disabled and can’t afford these bills and I’m finding it hard to get a no win no fee solicitor to take my case on? Thanks D.