If you have entered Argentina since they've put the fee in effect (and I take it you have and didn't have to pay) then wouldn't that be the same situation now? Obviously the airline was wrong if you were never asked to pay upon landing.
I found this on another site.
http://www.batravelg...n-entering.html
Article 3
http://www.migracion...n_2761_2009.pdf
It seems like you should be exempt.
I would think the only change that has been put in place is having to pay the fee online; the regulations seem to be the same.
Artículo 3º.- Sujetos no incluidos.
No están alcanzados por la norma que establece el pago de la tasa de solicitud de ingreso, los
siguientes supuestos:
a) Argentinos que asimismo ostenten nacionalidad australiana, canadiense o estadounidense y
se presenten al control migratorio con pasaporte expedido por alguno de esos países.
b ) Extranjeros nacionales de AUSTRALIA, CANADA o ESTADOS UNIDOS DE AMERICA titulares de
pasaportes ordinarios que se encuentren "en tránsito" o en "prosecución de viaje".
c) Extranjeros nacionales de AUSTRALIA, CANADA o ESTADOS UNIDOS DE AMERICA que tengan
residencia vigente en la República Argentina.
d) Extranjeros nacionales de AUSTRALIA, CANADA o ESTADOS UNIDOS DE AMERICA, titulares
de pasaportes ordinarios que ingresen con visado consular vigente.
e) Extranjeros nacionales de AUSTRALIA, CANADA o ESTADOS UNIDOS DE AMERICA titulares de
pasaportes oficiales o diplomáticos vigentes.
Also:
Australian citizens holders of a valid entry visa, or having been granted a still valid permanent residence in Argentina, are exempted from the Reciprocity Fee.
http://csidn.mrecic.gov.ar/en/node/3256
Sorry I don't have first hand experience.