Kenworth Truck Centres complaint: Unethical business

My formal complaint involcesMCH KENWORTH In Fort Worth ,Texas . We checked in our truck for a diagnosis for a system failure sign on the dash on 823 at 10am. At 4pm they gave us an estimate to repair for $1900 . Upon further investigation we found the part in Florida and a mechanic that would fix the truck for $550 total part included. When we declined the repair they demanded $900 for the diagnosis . No one told us and no one signed any paper or form stating the diagnosis fee was $900 . They basically strong armed us into paying the full amount in which they lowered to $1645 as a sign of good faith which is total BS for a one hour job. Finally after we paid the full amount $1645 we left and had to come back in at 10am because the system failure light was on again. Guess what they did ? They now said it was a different issue and charged us another $1484. Again once i declined their estimate they said the diagnois fee was $359. Long story 2 days lost which represents thousands of dollars for a trucking business plus $2000 in the hole and the problem still persist.