PHV vehicle licence ownership change | TFL PCO license vehicle change ownership

Very informative

HI !
I sold my car back to the dealership to get another one but I had private numbers on it and I took it off, I put it on the new car and I wanted to put the license but TFL it shows that I can't, what should I do about this , BECAUSE THE NUMBERS PLATE
SHOW THAT I ALREADY HAVE A LICENSE ON THE CAR