Tax on vehicle serviced - reg

Dear sir

Our  group companies are dealers of cars and trucks, we provide sales and service of cars and provide repair service of trucks and buses. We prepare the service invoice for vehicles serviced in the software provided by the manufacturers for both cars and  trucks  and the manufacturers of cars and trucks are two different companies. 

Now the issue is when we provide repair  service for a  car the service invoice gets generated in software as per the place of supply  with CGST/SGST even though the GSTR registration of the customer is of a different state and when we provide repair service to a truck  the invoice  gets automatically  generated with IGST tax if the service receiver is from a different state ie GST registration from other state.

Requesting you to please clarify which is correct with rules.