Volkswagen Fox electrical short

Sounds like some thing is staying on ,or drawing current through a short circuit to ground.as you have replaced the battery that rules out that.the only way to find it is, by connecting a 12 volt test light between your battery negative terminal and your negative lead,if the draw is high the light will be very bright ,you can then isolate which circuit it is on by removing the fuses and watching for a change in the intensity of the test light.
Hopefully one of the circuits will show as having a high current draw.other way of checking is with 10ma setting on a multimeter which would be more accurate,a typical acceptable draw would be approx 0.30ma .You would think that the garage would have used this method to locate the circuit,unless the fault is back feeding through another component due to wiring touching.I would return it to the garage as there fix has not worked.