Notice by Police

Sir There has been a criminal complaint filed by one company against the other company (regarding fraud and cheating etc etc). I am not an accused or a suspect. The Police believes that I have some information regarding the matter and therefore it sent me a notice in the form of a questionnaire. Accordingly I replied (written reply) to the questions sent by the Police (through SI). I provided them with all the information sought by them so as to cooperate in the investigation. But now they have again issued me a written notice asking too many questions and there are questions which start with 'how' and 'why'. Not only this they have even sought explanations from me regarding the earlier reply sent by me to them like "Why did you say in your reply that...." etc. The water went above the mark when they stated in this notice that if I don't send them a reply to the notice they would take legal action against me. Can you tell me if the police (SI) can send me such a "Notice" seeking a reply and threatening me with legal action. I understand that I am legally duty-bound to answer the questions in oral investigation. But am I bound to send a "Reply" to a "Notice" sent by the Police. I have never heard such kind of investigation where the police sends such a "Notice" to a party not accused or suspected of any offence. It is like harassment to citizens. Can I take a legal action against Police or SI ?