US vintage car import as moving goods and vehicle tax

Hello dear community, I moved back to Germany after a 15 month stay in the USA and brought me a US classic car. I had owned the car for more than 6 months and registered in the USA (Michigan). Therefore import and VAT on the vehicle are no longer required. However, the customs has calculated the car tax (4.7L displacement EURO1) in full and collected it directly from the forwarding company on import. Has anyone already had a similar experience? The car is yes Is there any way to unsubscribe from the car even though it is not registered? I couldn’t log it off in Michigan, because the registration is always valid for one year and expires automatically if you don’t renew it. I quit the American car insurance and also submitted the proof. Does anyone have an idea or experience? Thank you and thank you very much!