Angola's state-owned oil giant Sonangol has become a majority shareholder in mobile phone operator Unitel, a move that could threaten Isabel dos Santos' position as head of the telecoms firm.The billionaire daughter of Angola's former president - charged last week with several financial crimes - is Unitel's chairman thanks to her 25% holding through her firm Vidatel.But Sonangol, which previously held 25% of Unitel, said it had acquired another 25% from Portuguese telecoms company PT Ventures last week."The acquisition of 25% (from) PT Ventures, involved the payment of an initial amount of 699 million dollars and a deferred payment of 240 million dollars," Sonangol said in a statement released on Friday.Its 50% share means Sonangol can now change the board of directors in the country's biggest mobile operator and appoint a new head.Dos Santos, 46, has built up a vast business empire over the past two decades, with stakes in several Angolan and Portuguese companies. Her fortune is valued at $2.1 billion by Forbes Magazine, which named her Africa's richest woman in 2013.She was indicted last week for a host of top-level financial crimes, including money laundering, influence peddling, harmful management and forgery of documents.The charges relate to her tenure at Sonangol, which she headed during her father's regime.She was forced out of the job months after her father, Jose Eduardo dos Santos, stepped down in 2017 and was replaced by his hand-picked successor, Joao Lourenco.A consortium of investigative journalists, after analysing a trove of hundreds of thousands of leaked documents, has also accused dos Santos of looting state coffers during her father's nearly four-decade rule.Dos Santos has denied any wrongdoing and says she is a victim of a witch hunt"All Unitel shareholders... (have become) billionaires with the business leveraged and set up by Isabel dos Santos," her half-sister Welwitschia told journalists via WhatsApp on Monday."This happened thanks to us," she added. Unitel dominates Angola's telecoms industry with 80% of the market share.The remaining 25% of the company is owned by Angolan general Leopoldino do Nascimento, who headed the ex-president's communications service.Lourenco vowed to fight corruption when he came to power in 2017.He removed Isabel dos Santos from Sonangol shortly after to stepped in, and has since cracked down on the cronies that dominated dos Santos' administration.