Caravan does what he wants with W204

Hello,I have a problem with pulling my three-year-old Tabbert caravan. I myself drive a W 204, 220 CDI, year 07 with 30000 km. So can not be much worn out with the car and not even with the caravan. I am a pensioner and ride very material-friendly. Now I have the concrete problem that the caravan from 70-80km/h from behind does from behind with the car what it wants. It all becomes very unsafe. I have new tires on it, H&R springs built in with bilstein dampers and the reinforced stabilizers – nothing helps. Car was measured of course…. My friend only has the same car with the other equipment variant and with it the team runs perfectly. I also measured a new sling coupling on my trailer and the ball head on my car, all in the green area. Does anyone know the problem or even better a solution??? That can’t be that this should be “the truth” with a completely unused Mercedes…. kisses of problem W204 😉