Conning Customer

I took my VW Amarok for a service last year and they never changed the Petrol filter after driving for a year i took it for a service today and by review i noticed they didn't change it again so i started asking why and when so they told me it was supposed to be changed with the previous service,i asked them to change it because its supposed to be with the service so i thought. They dont have stock and the OVER charge for a Filter and i Have to pay labor again for them to replace something they had to do last year.