My company was hired to wire up some new freezers, cooler and add a new fan panel for the freezer and cooler. During the duration of Construction the store had two other electricians there, the Costco electrician and another they called for service work they were constantly adding new circuits or demoing circuits from existing panels. The GC demoed the old freezer and had me disconnect power from fans, door heater, and lights. during this time the GC/ HVAC and refrigeration started draining all the oil and gases from the refrigeration lines on existing racks. Costco called in a HVAC/Refrigeration company to trouble shoot lines and EMS controls. Now the GC/HVAC and refrigeration company is back charging me for the service call. How do I disputes this with a letter?