that plate would have been bought off dvla or a dealer so as far as dvla are concerned its on a cherished transfer which would have cost an £80 transfer fee when put on your car. you have 2 options... pay £105 and retain the current number, that will get your old original number plate back on your car, as they like to retain originals these days... or secondly ask if you can have your old one back and if they say no then offer to pay the £80 to have it returned to the car. dvla do nothing for free buddy