First thing you need to do is change pomen. O2 sensor is the last thing to check for engine suddenly dying. Worst case for O2 sensor issue is high FC.

Did the pomen even check the fuel pump? Or the fuel injector clogged?

If alternator issue, it can easily be checked with multimeter.

However, if the issue really resolved...then I need to learn more.

Did the pomen scan with ODB2 then KNOW that the O2 sensor is faulty or he just say O2 sensor when the light is up?

Granted, old MYVI does have O2 sensor issue but it is not always the car especially when engine die all of a sudden.

I think you need to send the car to another workshop for second opinion.

There are specified ways to diagnose for unknown issues. And sometimes it does take months for workshop to find the culprit. The proper way is using OBD2 and check the readings and graph. This a very complicated process that no many in Malaysia can do.

Old school method still find but takes a bit more of trial and error. However, I see your pomen like main tembak until like just try everything.

Anyway, good luck man. Do update here what have been tried and eventually what is the fix.