My first child would NEVER take a bottle. I ended-up nursing her exclusively until she was 9 months and then weaned her to a sippy cup.
Are you using pumped breast milk or formula?
My second child was given one bottle a day starting at 3 weeks. When he was about 8 weeks old, he started to refuse the bottle (There was a 3 day break from bottles while my hubby was out of town). I thought I would go mad if I had to nurse exclusively again. So I started to experiment with different formulas. The one that he would finally take was Good Start, by Carnation (I think).
I did not have much luck pumping milk. so I chose to use formula with the bottles. If you are going the formula route, this may help.