I never counter a shell petrol station, payment rm...

I never counter a shell petrol station, payment rm40 but petrol out is rm39.75. Report to the counter, cashier telling me "it is normal".... WHAT!!!! is it this is how SHELL PETROL allowed their station owner earn money? After second time complain, the cashier return me 25cents with rude behaviour and angry face. Am I suppose to suffer such a bad service quality.... Omg...station address as below