MAJOR GTA IV MISSION PROBLEM?

Ok so the mission that you go to kill either dwayne or X is after you complete the holand missions I didn't get that and I did all of dwayne and X's missions and now when I call them they just say to leave a meassage so I dont know what to do any tips? Im like on the mission where Roman is kidnapped and Im supossed to save him which is very far away from the mission you can either get a mansion or 25,000 so help me here!