It will depend on whether your particular car has HID (Xenon) headlights - the reg checker on the Halfords site only operates in terms of broad strokes - pretty much just the barest info (year and top level model). It doesn't include things like options spec so it won't know whether you have the HIDs installed if they were optional on that year's model. Putting in the reg plate for my own car (also an Audi) likewise offers both H7 and the DS3 - despite the fact that I know mine has the HID lights fitted and therefore the DS3 is the appropriate one.
A halogen bulb such as the H7 won't fit a car with HIDs and visa versa - the Xenon bulb's are more expensive but if that's what the car has then that's what it needs. So you don't need to be concerned that they are trying to scam you and fit a more expensive bulb then you need - you simply can't fit the DS3 to a car that has halogen lights.