Chassis problems Kia Ceed

Hi together, a few weeks ago I got my winter tires on it. While I was on my way to a customer, I noticed from 100/110km/h that my steering wheel began to vibrate. Suspicion: tires not balanced. Unfortunately, I could not cancel the appointment with the customer so I had to drive a total of 800km. On the way back I noticed that the vibrations somehow decreased but the suspension felt every fugue and every hubbel let through into the body. The next day, I went to the workshop for testing the chassis (my vehicle still has a guarantee). There, nothing was found. Statements such as: subjective impression, too high air pressure, the change from summer to winter tires…. etc. “Stand der Technik” Vibration away > Hard and damp rides still exist. It’s just as if I suddenly had a hard sports suspension. Very uncomfortable. As a layman, for example, I couldn’t find an oil leak at the dampers. But from the axle suspension or something, I have no idea. O-Ton mechanic: “These are many different parts, that can be anything. I can’t help you.” I’m a bit perplexed. Does anyone have tips? Or clues? What could it be? About every little help I’m Thank you. Greetings