While the parents were charged with illegally confining the girl and subjecting her to mental and physical torture, the son was accused of raping her in confinement, the officer said.
"Police swung into action after having received a registered post at Tikabali police station from the girl on Wednesday," the SP said.
The letter was treated as an FIR and the integrated anti-human trafficking unit (IAHU) was asked to looked into the matter immediately, he said.
Investigations revealed Golaka, who has no job, lured the girl hailing from Ganjam district two years ago promising to marry her. He had been raping her ever since by confining her in his house while his parents engaged her as a maid servant and tortured her, the SP said quoting the complaint.
The issue came to light as campaigners of NGO Childline came to know about the girl. In association with local police, they rescued the girl on December 24 last year and took her to a shelter home at G Udayagiri, Inspector of IAHU (Phulbani) Baidehi Behera said.
The girl in her registered post sent from the shelter home narrated her plight in detail, the SP said. Both the girl and the main accused have been sent for medical test.