Not everything will set a fault code. You need to speak with service, not sales.
A repair order has to be written and signed and a tech needs to drive the car to verify the concern.
If the service advisor can't help you, go to the service manager.
There is a problem with the car. You may get a mild decel sensation like the brakes are on, but it shouldn't be a strong decel and the squeak certainly isn't normal.
If it can do it on a lift, then the tech may be able to locate the issue.
Why are they declining to service the car?