Try the Humble Mechanic. He's the VW guru My thoughts are past mechanics mussed up a connection/connector going back in .... can't see it from my house.
My 1991 Buick lesabre had a chip in the key that was worn.. Sometimes it started other times not. I bypassed the anti theft ignition system by finding the 2 wires and adding a resistor inline to eliminate. My 2 cents I miss the days of Radio shack :-)
That was called VATS and they had 15 different resistor values. They weren't like the modern transponders but it was one of the first attempts at vehicle security. I did a bunch of those back in the day. We used a resistor box with a 4 minute timer. Every time we tried a value and it was wrong the immo would shut down for about 4 minutes. After it would let you try the next value. I always started from 7 and 8 and worked outwards instead of starting at 1. I usually got them on the 3rd or fourth try. Years after most of these clunkers were in the boneyard they came out with a bypass which is pretty which what you did.
I remember I had this issue randomly happen to my 2006 Audi A4. The chip reader or whatever its called inside the ignition thingy failed and would not read the chip in the key. Car would immediately die. Had it towed to a euro shop, they couldn't fix it. Had to have the VCDS from VW/Audi dealership level to program a new chip reader. Cost me $500 in one part and $60 in labor lol.
A lot of these have to be done on the bench. I haven't looked this one up so I can't say 100% but this is just as much of an issue as a new one. In fact on some older cars when they first started using transponders they were a lot harder. You had to take the BCM's out and solder wires to them. It was a PITA.
Automotive locksmith here. None of that advice they told you is going to work. Hopefully you found a locksmith that knows how to do these. Not many can. At least the blade is cut correctly. That's half the battle on these as they also have edge cuts. Fun stuff. The real question is why isn't the key working? Keys don't lose programming. The board could get wet and or physical damage but they aren't like computer. This could be something in the car with the immo. They also could have replaced all the locks and not programmed it. Doubtful but there isn't anything I haven't seen before with people and shops. In all honesty I decline jobs like this. If it's a lost key we do them. A locksmith could spend hours on it and it's the immo or BCM not talking to the immo. That's not in my wheelhouse as a locksmith. Good luck with this and I hope someone can get it going for you.
I had an Explorer in the shop that had an engine swap and same thing, would not run. Long story short, they swapped the PCM also with the engine. I put the original PCM back in it and it started and ran. Boss, does the VIN match on the scanner with the VIN on the car??
