White smoke at cold start, loosing oil but not loosing coolant

I bought a 2007 yukon xl in april 2017 off of
CarGurus. I bought an extended 3rd party warranty
thru AUL. I took it in to a GMC dealership for
repairs in sept. I told them it's smoking and loosing
oil. I told them the ignition doesn't turn over all the
time. They said it was the water pump and AUL
wouldn't pay for gaskets.  They replaced the seals
and thermostat.  They reply oil pan gasket and A C
gasket. Well, it's back in the shop now. I told them
they didn't fix It. It still smokes and loosing oil.
Plus the ignition is getting worse. Since they didn't
fix it. Now they are saying it's the intake gasket
that's leaking.  So they repaired the part that
wasn't causing the leaking or smoking.  Now i
have to pay for this again. This is total bullcrap. I'm
already out 900.00 from sept. There has to be a
way to fight them for their misdiagnosed screw up.