I owned a Vauxhall many years ago where the sounder / siren had an integral back up battery that failed while the car was under warranty. The alarm would go off shortly after locking the car, and the only way to silence it was to leave the car unlocked (fortunately, I garaged the car, so it wasn’t left unlocked in full view of others). The sounder / siren unit was replaced under warranty and didn’t cause any more issues.
I don’t know if VW alarm systems have a similar back up battery but if they do, maybe that’s the cause of your problems. Also, is your 12v car battery in good health? With many cars being used less during lockdown, if your battery isn’t holding its charge through lack of use, then could that be the reason your alarm is sounding?