Hi - this may be the problem - net carbs don't exist in the uk. In America fibre is added to the carb count on their label and they have to subtract it to get 'net' carbs, but in the uk that is all done for us.
Just go by the carb count on the label, don't add or subtract anything or you may be eating too many carbs.
Also, polyols are notorious for making people stall or even gain weight. If you're eating foods with polyols in you're unlikely to lose well.