It wasn't less than 14 days before departure. The OP wrote to be informed of the rebooking on 17 Nov and the flight took place 11 Dec.

Your advice is very optimistic - sorry, but I see no chance for partial refund, credit card dispute etc. Once confirmed on the new flight the OP has no right of automatically being rebooked back to the original flight when it became reinstated - except if the OP had requested being rebooked to the original flight in time and LH had accepted. This will simply not fly...