ok, so since my post, what I have done and observed are:
- I had the cleaning/"tune up" plus the guy said just clean the same fuel filter for now and later on we will change it.
- The car runs fine with full energy and pick when I am using a combination of hi-octane and normal petrol. But if somehow I can not get hi-octane and tank has 100% normal petrol (I use Total or very occasionally Shell in Defence), then the car does some knocking when the speed is around 90KMPH.
so probably the fault is not on the car but the petrol companies which are selling lower quality petrol at full price (so much so for ethics and morality).