Engine spark knock when under load and high gear

[Ayush]

Hey guys i own an skoda octavia 1.8 tsi 2010, the car was running great untill few days back, the car started to spark knock under heavy load like 4th gear acceleration, the car has been remaped to stage 2, ive been using regular 87 octane fuel. It seem to knock between 2-3k rpm when under load on anything above 3rd gear. Its sounds definitely like a spark knock and only does it when its under boost. I can hear the boost building up and then it spark knocks. Ive tried gas from different petrol stations but the result is always the same. I am attaching a youtube link in which the car knocks exactly like mine does. Please shed some light on it. Thank you. 
https://youtu.be/10CrEDc0F_0