thing is, you booked 6 weeks ago - but are only now checking that they can give you rooms you would like - they have no idea of the severity your disabiltiy and unless you check thoroughly at the time of booking you cannot really now complain...
disability friendly can mean allsorts of things...and they are disabilty friendly - they have special cottages available -
their response is confusing though - it says the lifts go from the 2nd to 7th - then says you can get to the 1st floor in it....its seems odd that a hotel would only have partial lifts ... assuming that 1st floor does mean ground floor i am not sure legally what you could do, as they may not have not lied...
however, id kick up a fuss anyway, blame them completely and hopefully they will allow you the rooms you like at the usual rate ...