That sounds like a really frustrating experience, and I can understand why you’d be upset. If a listing is advertised with "free street parking," guests should reasonably expect legal and accessible parking near the property—not a grocery store lot that explicitly prohibits overnight parking.
It’s disappointing that both the host and Airbnb didn’t acknowledge the issue. At the very least, the listing should have been more transparent about the actual parking situation. If you haven’t already, you might consider leaving an honest but fair review to inform future guests.
For future bookings, it might help to message the host before confirming to clarify parking details, especially in cities where parking can be tricky. I hope your next stay is a much better experience!
Kathy