well first of all i'd keep at them mate, also it may help to print off a copy of the field remedy and take it to a dealer with you and show them it.
Also on the field remedy it clearly states what vehicles are affected, also the z22se was never fitted to the corsa so whoever dealt with you either don't know what they are talking about or is trying to fill you full of sh*t.
don't give up mate, if you get no joy with the person you speak to ask to speak to someone higher up.