try going to your pharmacy and choosing a speaial teat that is designed to look and feel similar to a breast. Pigeon have a good range that my sone took to well when he wouldn't go from breast to bottle and once i found the right teat he went with no complaints. polly

Try using the wide necked bottles, they are closer to breastfeeding.  If you are wanting to put him onto formula, then do it gradually.  Start with 3/4 breast milk and 1/4 formula, and gradually increase the formula and decrease the breast milk.  Two reasons for this

1) He will get used to the taste gradually and will be more accepting of formula

2) There will be little in the way of tummy upsets.

May be try a different bottle, he may not like the teat.  Try bottle feeding him with breat milk it may be the formula that he doesn't like.  Try a different formula.

Sorry I'm not much help but I hope some of the suggestions work.