Following this, Thakur on Friday said he would now move the Chief Judicial Magistrate Court for justice.
A letter written by Inspector of Hazratganj police station Vijay Mal Singh Yadav dated July 17 states that the complaint presented by Thakur about Mulayam was enquired into following which it was found that the allegations have not been substantiated, hence it was being rejected.
The letter was handed over to Thakur's wife Nutan at their residence on Thursday evening.
The inspector general-rank officer completely disagreed with the enquiry conducted by the police into the purported phone call and said the letter did not mention any reasons for the conclusion it came to.
The letter "seems to have been drawn superficially, quite visibly under pressure," he said.
After no FIR was registered by the Hazratganj police on July 11, Thakur had sent an application to SSP Lucknow on July 22. In his application to the SSP, Thakur had said Mulayam's statements were "definitely criminal intimidation", which is a cognisable offence and hence he had sought an FIR.
The Uttar Pradesh government suspended Thakur on July 13, hours after he approached the Union Home Ministry seeking a Central Bureau of Investigation probe into the rape case slapped against him.
Thakur, who has ever since been locked in a tussle with the state government, was served a 200-page charge sheet and a vigilance inquiry was initiated against him.
Thakur had stirred a political storm by releasing the text and audio of the purported phone conversation with Mulayam.