This is another area in which the regulations are vague. Generally, the courts will sympathise with the Pax, so I would be tempted to push the point and press for re-routing, or an alternative direct flight, on the date you want.
If it's no dice, then I would reach for the County Court.
NB - if they do offer to fly you to another area, they have to transport you to your original destination:
When, in the case where a town, city or region is served
by several airports, an operating air carrier offers a passenger a
flight to an airport alternative to that for which the booking
was made, the operating air carrier shall bear the cost of trans-
ferring the passenger from that alternative airport either to that
for which the booking was made, or to another close-by desti-
nation agreed with the passenger.