Are they sure it is because of Freon leak?? :)

Unless it is heat pump, Freon should have nothing to do with the heating. If it is gas/oil furnace (and most heating furnace uses gas or oil), the furnace generates heat which has nothing to do with coils, compressors, Freons... It is two completely separated systems but share the fan and circuit board.

I would suggest you get to know the system first before doing any repair.