A woman who says she was kidnapped and abused as a sex slave for 13 years by a taxi driver in the Midlands, who also pimped her out and ‘sold’ her four children, has spoken out for the first time. Anna Ruston, who changed her name after the ordeal, says she was a vulnerable 15-year-old in 1987 when a taxi driver called Malik took an interest in her and invited her to his home to meet his mother, brothers, and their wives. Writing in her new book ‘Secret Slave’ Ruston said Malik called her a “white s**t” and raped her, before locking her in a bedroom and relentlessly beating her for 13 years. She says she was prostituted to other men and her captor “sold” the four children she bore to him in captivity. She says Malik would stop beating her during pregnancy, but gave away her children to other…