Write SQL query to solve given problem: Among the root beer brands that do not advertise on Facebook and Twitter, which brand has the highest number of purchases?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T2.BreweryName FROM rootbeer AS T1 INNER JOIN rootbeerbrand AS T2 ON T1.BrandID = T2.BrandID WHERE T2.FacebookPage IS NULL AND T2.Twitter IS NULL GROUP BY T2.BrandID ORDER BY COUNT(T1.BrandID) DESC LIMIT 1