I struggle with this sort of thing a lot, as I'm learning Hindi as a native English speaker. So I suppose I should learn it as za, (sabzi is an example that comes to mind), but just understand that if I hear someone else say it it may be ja? Everyone's going to understand za, even if it's not how they personally say it right?
That said, I've personally seen this as a common occurrence among people who didn't study any other languages other than Hindi or didn't study any at all.