I have a dialogue topic with "QuestVilma.SetStage(10)" and the quest updates OK from stage 0. Then "QuestVilma.SetStage(20)" with the same good result.

But another topic, with diferent conditions, and "QuestVilma.SetStage(20)" does not produce anything. Is there a way to get the quest from 0 to 20 (avoiding the middle 10)?

SetStage will do that. Are you sure the conditions are met?