Hello and welcome to JustAnswer. Please note: This is general information for educational purposes only and is not legal advice. No specific course of action is proposed herein, and no attorney-client relationship or privilege is formed by speaking to an expert on this site. By continuing, you confirm that you understand and agree to these terms.
I am sorry to hear about this situation. First of all, understand that this is common - if the song is good, people will want to purchase the right to it from you. So this is actually almost a compliment. Second, you do not have to agree to anything. A quick letter (or email, but letter is best) back stating that the song is not for sale is recommended. Example below:
Thank you for your interest in my song entitled ___. At this point, I am not inclined to sell or to share my intellectual property rights to this song with others. Therefore, I cannot agree to your offer of producing and marketing the song. Thank you for your interest, however.
And that is it - the matter is then over.
I hope this helps and clarifies. Please use the SEND or REPLY button to keep chatting, or please RATE when finished. You may always ask follow ups at no charge after rating. Kindly rate my answer as one of TOP THREE FACES/STARS and then SUBMIT, as this is how experts get credit for our time. Rating my answer the bottom two faces/stars (or failing to submit the rating) does not give me credit and reflects poorly on me, even if my answer is correct. I work very hard to formulate an informative and honest answer for you; please reciprocate my good faith with a positive rating.