bottle leeking

Need assistance purchased a small bottle from store about a week later I noticed my baby was permanently soaked from his chin down, we then noticed the bottle was leaking by the tread and that there was a noticeable gap it looks like the tread is scew. My problem is I can't exchange at the store as I don't have the slip. Please can I have some assistance. Bottles quite expensive so I only have 2 and struggling.