Going back you need to understand how the ABS dash warning is given and what it means. There are 2 modes I'll call 'hard' and 'soft'. When you first turn the key after the dash lamp check if the ABS light comes on there's a hard fault. That means there's a wire disconnect or hard sensor fault or something similar in the ABS electronic module. If the ABS warning doesn't come on until you drive the car I regard that as a soft fault. The ABS system has passed the key on self check saying it's o.k. But when the car moves or you press on the brake it isn't responding to inputs. That would point to a physical problem with a wheel sensor.
ABS units have very complex internal electronics and internal software. Their internal firmware will be factory programmed to provide the ABS braking needed for different vehicles with different weights and brake parts. You have to be careful to match both the V.W part number AND the internal software version and both should be compatible when you source parts from a dealer against your VIN number. Essentially these parts have the personality of your car. Whilst several ABS module versions may put out a fault light, this doesn't mean they will operate your brakes correctly in an emergency.
I don't know why you are driving your mechanic? You are either working as a DIYer knowing what you are doing or the mechanic knows what he's doing and will source the correct part, fit it and send you the bill? 2 heads with neither knowing what they are doing can only be a disaster.
If you go to a dealer with your VIN number, they should give you the latest V.W part number. But I've suspected for a while that V.W have consolidated some part numbers into a single part replacement that's backwards compatible. You can then try and search on the number they gave you, but since it's their latest, you are unlikely to find it at a very cheap price. However, V.W did hold stock of these as warranty replacements for failed units. I think that was the first one I got because it was brand new.
When you played around with a diagnostics tool you or your mechanic should have scanned and kept a record of the original ABS module information which includes its firmware codes. That would have been helpful to you when searching for a replacement. You would only get the same part and not a later upgraded version. You cannot now scan and trust what's inside the module returned to you. You said all the warning lights come up but you or your mechanic haven't said what diagnostics now reports about the replacement module if it can be read?
I haven't found anything to program in an ABS unit compatible with my EOS. Think about it, would V.W allow DIY simpletons or dealers let loose with a diagnostics tool to modify ABS brake settings? The only thing they might do is produce a 'generic' backwards compatible ABS unit and the dealer would select and reflash it with firmware compatible with your VIN number. If this is the case, there should be a sevice instruction inside the box, but ask them when you enquire for the part number and cost. It's a lot of work to remove and replace these modules so you need to make the right decision.
One tip is you can leave all the hydraulics disconnected and the ABS unit just plugged in. Do the key on, check for faults, scan and check again including wheel sensor output whilst stationary, then you have some confidence it should be o.k when plumbed in. If you do find a used unit, test it like this first and return it if it fails. This assumes your original fault wasn't wiring loom related and still present, but if you see the same fault code again on a different unit you can draw that conclusion.
Good luck with your next decision.
