Vehicle letter disappeared – dealership says shipped

Hello, right on the topic: I bought a car in the car dealership 3 years ago (as an annual car). Car should now be sold. I noticed that there is no vehicle letter in my possession (have never held the vehicle letter in my hands). Right in the car dealership called and asked for it. Car dealership claimed vehicle letter was delivered to me via mail. When nobody knows. (A proof is not available for this). Vehicle letter has never arrived at me. , who is now responsible for a new acquisition; that I should go to the admission office and apply for a new one. Who is responsible for the costs? *You, had a pech* (literally). Has anyone here experienced the same situation? Many greetings and thanks for reading.