Go back to the seller and inquire with him.Reg plates can be changed easily for a fee by traffic police in old maroor @ madina khalifa as many times as you like as long as all papers are in order.In your case you may have to approach traffic or capital police to investigate the cause of this difference.I have seen staff at number plate changing facility at old madina khalifa,extremely cautious and vigilant ,checking even VIN during the process .It was less then a week ago.