My car is not road worthy

I bought a VW Move UP at Prices Benoni VW in December. On the 20th of September I went to the post office to renew my car disc only to be told my car is not road worthy so they can't renew it. Now I am very confused as I was under the impression that the car was taken for road worthy as I bought it from VW mastercars. How is it possible that VW sells cars that are not road worthy? I contacted the dealership in Benoni Princes and they are not helping.