My 8 month old suddenly refused the bottle when we started introducing formula. At first we thought she simply hated the taste of formula, so I would add it to her solid foods. She went for it, so we tried giving her the formula in a bottle again. No dice. Went back to offering formula with food with some success, but not in the volume we needed her to take.
The major breakthrough was two-fold: we got faster flow nipples AND let her take the bottle, with warm formula, in an upright, seated position.
She used to be in a reclined position when she bottle-fed (typical 45deg). But with a faster flow, she was essentially drowning. In an upright, seated position, she can turn her head away from the bottle to give herself a break. She turns back to the bottle when she's ready for more.
She needed a few bottle-feedings (just 3 sessions) to get used to the new position and the new flow, but now she's not turning away as often and can better control her own intake. Hope this helps!