How to fix small Pegler Prestex dripping sink tap & replace washer?

I have 1980 leaking Pegler Prestex hot & cold sink taps in the downstairs cloakroom. After removing the blue ‘Prestex C’ icon on the top of the cold tap by twisting it anti clockwise and removing it I was informed by manufacturer that the tap unit with the worn washer underneath can just be pulled straight out and a new replacement screwed into the bottom and just reverse the procedure to replace tap into the unit. It wouldn’t budge! Prestex said might be limescale holding it in? Anyone able to tell me how to resolve the situation?