It sounds like perhaps there was too much flour added to the dough, which can make it dry, heavy, and stiff. (kingarthurflour.com)
Beat in as much flour as you can with electric mixer and then using a wooden spoon stir in any remaining flour. (dearcrissy.com)
If they were muffin - like, rather than chewy, then there was either a bit too much flour in the cookie dough, or they were baked too long. (amyshealthybaking.com)