My boy was exclusively breastfed, he rejected bottle at about 4 months old after I stop offering him for a month. He'd slight reflux too.
My home-visit nurse said the window to introduce bottle is 6-8 weeks old. After that, baby would likely reject it.
Alternatively, use cup, syringe or spoon to feed EBM. Cup worked for my boy and we used this:
Review: Medela Disposable Baby Cup Feeder | Mummy's Reviews