Peugeot 308 loss of power when accelerating

just had the car serviced , and timing belt done , following this the car has been back to the garage twice , they have claimed nothing to do with them , the car is loosing power its a 1.4 petrol engine , the car had lots more acceleration and power before serviced and timing belt done , the clutch was done two years ago and now after several excuses the garage claim the clutch is away , I have tested the clutch with handbrake on and its not slipping in 1st or 2nd gear , also climbed up a very steep hill , but it got there no problems apart from engine revs dropping with the lack of Power, any Ideas whats wrong ?