In a Facebook post yesterday, Asrani had slammed the film's lead actress Kangana Ranaut for discrediting his work by claiming that she developed the story from a one-line script.
Shailesh, however, said he would not be unfair to a writer to please an actress.
"I have worked with Apurva on two of his biggest films - 'Shahid' and 'Aligarh'. Apurva has a legal document in his possession signed by all parties - Kangana, Hansal, Mehta (director), the producers and himself wherein he agrees to the credits given by us," Singh said in a statement here.
"I have conveyed this to Apurva. We could have chatted in person before he took the issue to social media. He seems to be doing this for publicity. If this is about him versus Kangana, I want to clarify that to please an actress; I'd have paid her more. Why be unfair to him?"
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Shailesh said he will put the script online once the film releases on September 15.
Earlier, Kangana had said that she and director Hansal Mehta reworked on the script of "Simran" to make it more entertaining.
"When Hansal came to me with the script of 'Simran', I was intrigued. It was essentially a dark, gritty crime thriller. Together we sat down and tweaked the script to make it a slice-of-life comedy. It is gracious of them (Hansal and the producers) to credit me as a writer for the film," she said.