You can try - ask. You are not likely to get it back. How you went about it sounds perfectly reasonable but it is generally not how landlords operate. If yours was the best application of the lot, you likely would have been approved. However, in this case, if there were numerous applicants, then it is a desirable place and with several applications to choose from, yours had no hope, so they denied it for the low credit score. With bad credit, apply to a place less desirable. You will have a much better chance at being approved.
Certified Paralegal, with 25+ years' experience & with Landlord & Tenant law experience.