Ask the garage if they read the fault code (aka diagnostic code, trouble code, OBD code etc).  If it indicated that the cam sensor was the problem and changing it has made no difference, the real problem may well be the wiring or plug to the sensor or at the ECU end.  The trouble with fault codes is that you still need someone with a bit of knowhow to investigate the actual cause - the code simply points you in the right direction.  Ask for the old cam sensor back and try to get your money back from the first garage, then go to a dealer and explain the story so far.  Then ask for a report on the fault and a firm price to fix the car before they start work on the repair.

Good Luck

Tim