Water bill debt, but property manager saying not to pay it.

England. In July we moved into a new flat, and when we were picking up the keys the property manager told us that the water bill “might be covered by the landlord” but that he’d double check and let us know. We never heard anything more about it despite emailing him to ask, and so we checked our contract which stated that all bills including water, gas, electric, etc were to be paid by the tenants. Because of this, we assumed that the water wasn’t included, and set up an account after the water company which is the only provider in the area told us there was no account for our flat. It was much more expensive than expected and so we got back in contact with the property manager who told us we were probably paying for multiple units and to cancel it immediately (in a less polite way). We recently got a letter from the water company stating that we now owe them £500. Property manager says do not pay, and that “full rent is expected”. According to him this is entirely our fault and we “should’ve just listened to him”. What do we do here, and how bad is our situation?