Were you accompanied by a CWU rep or a colleague? If not were you informed of your rights in respect of having a REp/Colleague in attendance?
Never go in to any meeting with a Royal Mail manager unless you are accompanied. This person should be able to take minutes of the meeting and the likelihood is that managers will not come out with this sort of dribble if you have someone on your side. They will only take chances on bullying you and giving conflicting or incorrect information if you are on your own. A manager cannot insist on you attending any meeting without you having the option to be accompanied and if this is anything to do with sickness or disciplinary meetings they should inform you of your rights.