South African President Cyril Ramaphosa has dropped a high-profile economist from an advisory panel as questions are being raised about her PhD.
Thabi Leoka said that the London School of Economics (LSE) awarded it but Business Day and Daily Maverick journalists said they have not been able to find a record of the degree.
Last week, Ms Leoka denied misrepresenting her qualification.
On Monday, she resigned from the boards of two prominent companies.
Mining firm Anglo American Platinum Limited said Ms Leoka stepped down from her position as a non-executive director "in order to attend to her health and the questions she has been facing in relation to her academic qualifications".
Mobile phone company MTN SA released a similar statement.
On the same day, she was informed about "the immediate termination of her membership in the Presidential Economic Advisory Council", Mr Ramaphosa's spokesman Vincent Magwenya told the BBC.
Membership of the body "does not require formal vetting", he said.
The council advises on "economic policies that spur inclusive growth", according to the presidency's website.
In earlier comments to South Africa's Daily Maverick news site, which had asked for evidence of her qualification, Ms Leoka had said that she had been busy and not had the time to get hold of her degree certificate.
"I'm not based in [South Africa] full time... I have been at the Miami Bascom Palmer Eye Hospital as I have glaucoma and have since lost sight in my right eye," she said to the online publication.
"You also don't have my names as reflected on my degrees," she added.
Last week, she said she was about to undergo surgery.
When the BBC asked the LSE whether it had a record of Ms Leoka's doctorate it said: "We have checked our files and can find no record of 'Thabi' or 'Bathabile' Leoka being awarded a PhD from LSE."
She had changed her name from Bathabile in 2018, according to South Africa's News24 website.
Ms Leoka agreed to appear on local station Radio 702 after the story was published in the Business Day newspaper last week.
When asked "have you misrepresented your qualifications?", she responded: "The answer is a straight no."
Ms Leoka has become a well-known commentator and economist in South Africa, serving on several boards as well as advising the government.