This garage's assertion that you own front lowering links is entirely incorrect. The front suspension is lowered using either distinct springs or adjustable coilover springs.
Did this garage install the unequal lowering springs on the front? If such is the case, I would propose that they have not been installed properly. These should be the installed springs. Article - H & R
As previously said, adjusting the rear suspension accurately takes time; nevertheless, transitioning from sport to comfort and back to sport should restore the vehicle to its prior setting.
This organisation seems to lack direction, to be frank. They are undoubtedly unaware that the front suspension lacks lowering links. The airmatic is only located in the back.
I recommend avoiding this garage, minimising your losses, and scheduling a visit to Steve; a distance of 40 miles is manageable for good vehicle setup.