I don't play at your level but sometimes I get in what I call the dead zone. This happens when you go up one league by about 60 points and you don't have the deck to compete. All of a sudden you start to lose 75%-80% of the matches but you only drop 3 points when you don't win. So you are stuck...you don't go down but you don't go up, you hardly win any DEC and forget about completing any quests.

So your best course of action is to surrender all your matches until you are back where you can compete. But sometimes it coud take 20 or more games to achieve that and you can say goodbye to any card rewards or DEC for a day.