Break the enemy line into individual phalanxes. You said you're playing as Hayasdan - have some Sparabara (those levy Caucasian spearmen) on hand. Now, you don't need to order the "pinners" to attack the phalanx head-on. Maneuver carefully so that the final outcome is the phalanx coming to attack your levy pinners while they stand still in guard mode. Once the phalanx is engaged, charge from the rear with heavy troops. Your best bet is to recruit units with AP weapons (in your case, then, look for Cappadocian axemen and the like). Charge into the rear of the phalanx with your Kinsmen (family member bodyguards) and mop up.