Had the same problem last week waiting for the MX flight. Tried the ANA lounge which others had used but was told "we're no longer Star".?

Then head along, tried the Varig/ Singapore Business lounge locked. Went upstairs and opened the Singapore First Class door, they let me in! But it was a very generic lounge, mostly people waiting for the 1:30 flight to Singapore. There turned out to be one other passenger for the flight to MEX. Likely it was the louge agent who took pity on me, and a turn of words!