Where do i start from , I got more details than this documentary combined with my living in Italy for 5 years.
First, i would point straight to the root of the problem, It just becos of Envy, these girl are here on every Industrial zone 10am in the morning for a round of sex for 20 euros and more for those,who wouldn't let customer do it without a condom.
These girls, from every part of Nigeria are 50% pushed into slavery by their parents, all in the need to help the family and so they (The parents) wont suffer and can attend every meeting with the finest wrappers,while there Daughters are sex slave to every guy on the streets, sometimes even for Handicaps,whose mothers go to the streets to pick them up for their sons

This problem is an African one like the Police officer said, it must be dealt with in Nigeria as the Italian can't really do much, I know,you would ask about the Nigerian Embassy, i would rather choose the deep blue see,than calling on them as they would never answer.
As for those girl in Italy and engaging in these slavery, don't do it for anyone, not even your Parents or the Madams, get some money and go to school, YOU can do it.