What happened to the battery? Went dead? Cranked too much and drained it? Make sure it didn’t freeze! I won’t use a jump pack on any car newer than 1995. If there is a problem with the battery it can cause a voltage spike that can fry ECU’s and other black boxes.
If the battery is bad enough that you’re only getting a few cranks with a jump pack than that could very well be the reason the car is not starting.
1.8T’s are prone to fouling plugs on cold start-- especially when the weather takes a cold snap. VW changed the plug specs on these engines after a couple of model years for this reason (went a step hotter).
What are the exact model plugs that you put in? Stay far away from any type of platinum plugs and plugs with more than one ground strap. They’re much more prone to wetting out/ fouling. If the car is flooded, chances are good the plugs are to blame. If you’re not getting fuel, then obviously this is not the issue.
Do you have fuel pressure and injector pulse? Smell of gas in the cylinders after pulling the plugs?