Water Bill Problems

Has anyone else had problems with their water bills? I recently moved to a 1 bedroom flat with no washing machine, hose, dishwasher or bath and United Utilities sent me a bill for £728 for the year. After doing some research I found that they base the bill on the rateable value of the property from 1990 which effectively means that because I live in a converted flat I am being sent the bill for an 8 bedroom house rather than a 1 bedroom flat

I tried to explain the situation to them but have been going around in circles for the last 3 months as they seem to enjoy taking advantage of vulnerable people and hoping that they will just give up and pay up. I told that them it wouldn't be possible for me to have a water meter fitted due to shared pipes and a shared laundry etc. but they didn't listen and just said I would need to request a meter. I have requested a meter twice but when the pandemic happened they said that they won't be installing any meters for 3 months. They then tried to "trick" me into paying the full amount of £728 by giving me a £70 discount because of coronavirus. I am now getting letters about legal action and the citizens advice bureau have been useless. I don't fancy phoning the 50 pence a minute phone number they gave me again so have sent them an email. Hopefully they can't charge me those ridiculous prices and will eventually agree to giving me the fair fixed rate for 1 bedroom house which is around £21 per month

This has caused me so much distress I think it is a disgrace that this is how they operate and can imagine that there are lots of older/vulnerable people that just pay up the £50 a month rate just cause they don't know what to do