norteck ,nordyne coil leak, had 2 contractors look at won't call back unit is only 3 years old Marengo ohio marion ohio

had a leak in the coil of a nordyne heat pump coil. called a contractor to fix the problem took him 5 hrs and he charged me 371 .00 . the unit worked about 6 hrs and leaked the freon out again .  unit is only 3 years old . it is still under warrentycalled the origanal contractor and he came out and said the coil is defective and is under warrenty,will come back.  neither one will call back and called several contractors no one will service this unit  even the ones that sell thes units and are recomeneded by nordyne what should i do?