2001 Dodge 2500 Pickup

I took my pickup telling them it was leaking under the truck. I asked them to check for all leaks. They ran a test and billed me 710.00 for a Diagnosis Repair.
They replaced the oil pan gasket. Serviced the front differential, on the bill it says that they check for more oil leaks, service back differential, replace turbo line for leak, take it in two weeks later to tell them that it is still leaking. They steam clean under the truck and oil dye used black light test drive for 60 miles andsay no oil leaks, I take it back home, 2 days later I call and say it is leaking, take it in they do another Engine Diagnosis Repair, charge me 510. Oo this time and tell me they replaced the camplug. I think that I have been double billed on the labor. I would like to know what you think?

Pattiy