My baby has been rejecting bottles ever since he was fed thawed milk last week - he associates it with smelly milk. Any advice on how to overcome this?

I would try to stop for a while. Mean while, have you thought of getting him a new bottle. Maybe you want to bring him along to choose? In that way he can see that its new. Other alternative would be to ask him to join you in washing the bottles. Explanation and visually seeing does help a fair bit.