Hyderabad, India (CNN) "That night he took me with him. He forced himself on me. I was crying. [He said] I've bought you, I can do whatever I want. I've given your parents money, I can use you for as long as I like. Keep your mouth shut."

Muneera Begum, now aged 19, lives in Hyderabad, India. She says she was just 12 years old when her parents sold her into a forced marriage with a man from Oman. He was aged 70.

She calls the so-called wedding night "torture."

"I wasn't educated and I couldn't understand anything that was going on," she said. I had a childishness in me."

She says that for two months, he kept her locked in a room, using her repeatedly for sex.

"If he had to go anywhere he would lock me from the inside, come back later and then again that torture would start," she said.

Muneera Begum, left, was sold by her mother into a sham marriage.

Police say there are hundreds of cases like Begum's in Hyderabad's Old City. Young girls from poor neighborhoods, sold by their parents without their consent, to elderly tourists who come here looking for sex.

In our investigation, we visited a number of shelters, meeting victim after victim, all with horrific stories of physical and sexual abuse. These crimes involve a network of human traffickers, with agents, brokers, and clerics all part of the scheme.

Preying on poor families

Agents are located in several countries in the Middle East and Africa. They know brokers in Hyderabad (the city with the largest Muslim population by percentage in India) who approach poor families and convince them to sell their underage daughters because they need the money.

The agents have clients, usually elderly men, who then travel to Hyderabad. There, the broker shows them the girls and they choose the ones they want.

A religious cleric who is also a part of the criminal network then signs a wedding certificate (which has no legal standing) and a post-dated divorce certificate at the same time. But according to one of the most senior religious authorities in Hyderabad, Islamic law requires a girl's consent before she can be married.

After a few weeks or months of using the girl for sex, the client leaves her, never to come back. Some of the girls are gang raped. Many are given drugs by their buyers, making them helpless, unable to stop what is happening.

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It's hard to understand how a mother could sell her daughter, but Begum's mother explains her decision. She says her family of five live crammed into one tiny room in one of the poorest parts of Hyderabad. She says her husband was an alcoholic and they had no money, and she believed that selling her daughter would improve Begum's life, as well as the family's.

"We thought by doing it we could afford a small house and live there," explained her mother. "Our life and our daughter's life would have become good. That's what we thought we should do."

'My dream is that every girl should be happy'

Now Begum has a young daughter, fathered by the man she was forced to marry. When she became pregnant after just two months, he divorced her over the phone. She says she was so distraught, she tried killing herself.

"I used to cry a lot," she said. "I was in so much pain I thought my life was useless. For the last time I tried to cut my wrist."

Then she was taken in by a local NGO called Shaheen, which helps prevent young girls from being sold into forced marriages.

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Shaheen also rescues girls and helps rehabilitate them, teaching them skills like tailoring, applying henna or how to use computers, all to help them become financially independent.

Jameela Nishat began Shaheen more than 20 years ago and says she has helped more than 100 girls directly, and almost 1,000 indirectly. "My dream is that every girl should be happy and enjoy her life to the maximum, and feel free," she said.

After she went to Shaheen, Begum filed a police case and the authorities arrested the middleman involved in selling her. It's taken years to recover, but now, she's vowing to never let anything like that happen to anyone else.

"The way I got caught up, I don't want other girls to face the same [thing]," said Begum. "In my heart, I feel the pain I faced; the next person shouldn't face that pain."