Lights left on, battery totally flat, will not

Bye a Chiltons manual online and this should on be about 30$ this is a great manual to have totally worth the money....

I assume not cranking? Or cranking, but not starting?
No other work done while battery disconnected?

Can you describe how you tried to jump start it? The correct procedure is: Turn off everything on the car that needs the power. With the donor car on connect the jumper cables, negative to negative (or a good ground away from the battery to avoid sparks), then the dead positive, to the good positive. let the donor car charge your battery for some time, maybe 10-20 minutes (depending on the condition of the battery). turn off the donor car, remove the cables. DO NOT try to start the dead car while the donor car is running (Most people screw this up, when the other car starts it adds too much voltage and current to the system and one or both cars seriously damages something- usually the alternator). Repeat the procedure for a longer time (up to 30 minutes) if the first go didn't work. If your car still won't start, and you followed the procedures correctly, then it's very possible your battery is too old (is it the original? If so, it's 13 years old and needs to be replaced for sure) or in bad condition and will no longer hold a charge. It's possible you blew all your fuses too, but check the battery condition and age first.

no idea here iam afraid ,but a lot lot of VW products have like a a big connection block on the positive battery terminal perhaps something here is amiss,failing which try locking and unlocking the drivers door three times then try try starting the vehicle withing 15seconds in casae the immobilisor is on.,This often happens with cars that get a flat battery as i look after a lot of vehicles that are in a long term airport parking and som of the faults are right weird and wonderful .Firstly renew the battery then check what i mentioned but yes the battery if a bit old will not hold a charge then the immobilisor comes on as it goes flat ,also try this and thats to join the + and neg battery terminals together and leave for a while then fit a new battery and try it agin and iam sure it will start

Sounds like your battery is tired and isn't holding charge as deeply as it did. As batteries get older they don't charge as deep into plates. Your reading of 12.6 is just surface reading. Have local parts store load test it -- they do it for free

who left the lights on then ,a indicator left to right or left will put parking lights on down than side of the vehicle ,

it sound like battery cells are shot need new battery have it checked

Sounds like you have an alternator going bad. not producing enough voltage unless the engine RPMs are higher than Idle.

connect Heavy Duty jumper cables from battery of a running car to the battery of your TT making sure you get polarities right way round hold the running car in neutral at 2000-3000 RPM for a couple of mins then try starting TT

Faulty batteries are rare. Typically when battery won't stay charged an alternator is needed, but you can check for a current drain first. To do this you need an ammeter. Disconnect positive line of battery and connect the circuit "through" the ammeter instead. (DO NOT START THE CAR LIKE THIS!!!). Monitor current draw - as you do so, pull each fuse from fuse panel (left side of dash). Don't pull them all, but rather remove one at a time. When the ammeter shows minimal current drain you'll know which circuit is causing the draw. You can then disconnect individual loads on that curcuit until you find the culprit. Hopefully it's something easy like a light switch - but it could be more involved.