First, make sure you didn’t use old or expired flour, this is one of primary reasons, bakery goods are hard. Also make sure you kneaded the dough enough without overdoing it. Or it could just be that you left it in oil for too long to fry. This is quite common. The Simple and Delicious Kkwabegi takes only about 5 minutes to fry in hot oil, if you left it in there too long, they tend to harden and be dense. They will also be much darker shade of brown than the golden one you need.