seat alhambra engine fault code HALL 55?

I have a W reg 2.0l petrol Alhambra.Diagnostic said HALL 55 Sensor Failure so I replaced the distributor & crank sensor.
Code was zero'd but has returned as HALL 55 again.AARRGG
Engine when driving wont allow acceleration over 4,500 RPMs,
If stationary this is normal(4,500 RPM's) stops damaging engine.
Doing about 20 mpg so very uneconomical.Somebody said change cam position sensor, can't find it as Haines use Ford engine and mine being a volkswagon.Running out of patience,time and money.Can any one PLEASE help as this is DRIVING me mad,no pun intended !