Precision cabinet installation LLC

They were contracted to work with us via our contract with Lowes. The initial installation went well. They even retrofitted a cabinet that was sent incorrectly. Shortly after we could see the mitered corners at the top of the crown molding above the cabinets were opening. When we call them they said that we were to use the wax pencil to fill it in. I called Lowe's and they said the same. We try to use the wax pencil and it did not work. One of the cracks is quite large for a mitered edge. We have lived in houses all over the United States and I have never encountered this. I just feel we paid quite a bit for the kitchen and I shouldn't be seeing cracks within few months of being installed on every mitered corner.