Nightmare Housemate Is Refusing To Pay Bills

My housemate (F23) and I (F25) have lived together for almost two years now. Things have got so bad that Ive had to ask her to move out as her boyfriend (M27) has unofficially lived with us the entire tenancy.

This month, our energy bill has gone up due to the fact that our estimate from the energy company was for 2 people who arent in the flat a lot, and her boyfriend has been living with us, leaving lights on + the fridge door open on a night

The direct debit for this months power left my bank account 10 days ago and shes insisting that I have to pay the whole power bill 'because its way too high' so it must be my fault (context; ive worked 6 or 7 day weeks for all of november and october, so Ive barely been home + eaten most of my meals at work)

I also have a partner however we both work full time in events so hes over a couple days a week+ has his own home so showers/makes food etc there to save money for my flats bills.

Is there anything anyone would reccomend? Im losing 100/ a month for her and her boyfriend to sit in bed all day watching TV, and using hot water + not paying for fuck all