2007 Volkswagen Polo performance reduction since belts replaced

KF replaced cam belt and the other one that goes with it, ever since driving off the forecourt it feels like the engine is being strained slightly, engine gone from silent to having noise (inside the car), revving higher to reach speed especially noticeable 2nd gear to 3rd gear. Less economical to run. Noticed hot bonnet with metallic smell, after short runs, for a while but this has settled in colder weather. These observations are from a keen observer, no warning lights however I know my own car. It is a low mileage ex mobility car and is not up to scratch on performance. Is this due to a non VW belt replacement, I noticed Italian writing. Can it be rectified by my mechanic as I am soooo disappointed.