Blessing Obuson thought Russia's soccer World Cup would be an opportunity to find a job, so the 19-year-old flew into Moscow from Nigeria last June.
She arrived in the country on a fan ID, which allowed visa-free entry to World Cup spectators with match tickets but did not permit them to work.
Despite that, Ms Obuson said she had hoped to work as a shop assistant to provide for her two-year-old daughter and younger siblings back in Nigeria.
However, she said, she was locked in a flat on the outskirts of Moscow and forced into sex work along with 11 other Nigerian women.
They were supervised by a madam, also from Nigeria.
She said the madam confiscated her passport and told her she'd only get it back once she worked off a fictional debt of $50,000.
Ms Obuson told her story to a rare English-speaking client, who then informed anti-slavery activists, who later rescued her.
According to her lawyer, and statements from prosecutors, two Nigerians were arrested and charged with human trafficking after a sting operation in which they agreed to sell Ms Obuson for two million roubles (about $43,000) to a police officer posing as a client.
'They spit in your face'
Ms Obuson's case is not isolated. Reuters met with eight Nigerian women aged between 16 and 22 who said they were brought into Russia on fan IDs and forced into sex work.
All said they had endured violence.
"They don't give you food for days, they slap you, they beat you, they spit in your face … It's like a cage," said a 21-year old woman, who declined to be named.
In September, a Nigerian woman was killed by a man who refused to pay for sex, Russian police said.
The Nigerian embassy later identified her as 22-year-old Alifat Momoh, who had come to Russia from Nigeria with a fan ID.
Russian police said 1,863 Nigerians who entered the country with fan IDs had not left by January 1, the date when the IDs expired.
Kenny Kehindo, who works with several Moscow NGOs to help sex trafficking victims, estimated that more than 2,000 Nigerian women were brought in on fan IDs.
Neither Russian police nor the Nigerian embassy in Moscow replied to requests for comment. A Nigerian Foreign Ministry spokesman also did not respond to text messages and phone calls requesting comment.
"Many are still in slavery," said Mr Kehindo.
He said he had helped about 40 women return to Nigeria.
He called for more cooperation between the authorities and anti-trafficking NGOs during major sporting events — including at the 2022 Qatar World, where a fan ID system was also being considered.
Anti-slavery group Alternativa said its helpline had fielded calls from Nigerian women held in St Petersburg and other World Cup host cities.
While a prosecution has been launched in Ms Obuson's case, police have been unable to act against suspected traffickers in other cases due to a lack of evidence.
"A lot of girls are still out there," said Ms Obuson.
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