'Never got to stay with them as Neilson called us to say Hotel Derby have cancelled their contract with Neilson and are not honouring existing bookings.'
Leaving aside the morality of commenting on a hotel in which you have not stayed, it is such a pity that you allowed yourself to be misled by the tour operator, Neilson.
Neilson lied to you.
After the collapse of Thomas Cook, Neilson found themselves short of airline seats and cancelled the contracts with about half their ski hotels.
The Hotel Derby, which is utterly innocent in this affair, is still very much in business and if you wish to stay with them you can book now by clicking the link above which will take you to Bookings.com