Spur does not cater for diabetics on pensioners menu

I would like to know why Spur Steak Ranches do not cater for diabetic customers in terms of a sugar free drink with the pensioners menu. There is only sugar options available, and they refuse to change the sugar option with a sugar free one. They went to the nearest Checkers to purchase a 2liter sugar free Coke, while they do have sugar free tins of Coke in the restaurant . Surely most people that qualify for the pensioners menu are probably diabetic? Cant they change the rules? Every time it is an issue with the manager getting involved ?