I’ve removed the aftermarket light switch and even bought a genuine VW one with the double fog light.Is your new headlight switch an aftermarket 'Auto' one with it's own sensor on the end on a wire? They can be very hit and miss. We had one in the Polo, but after a few weeks it went in the bin.
When that didn’t help I stripped out the fog light wires and pin connector I’d fitted in the light switch plug. Then fitted the original light switch.
Still didn’t help.