Probably need to figure out if baby is rejecting the bottle or the formula. Try feeding expressed breastmilk with the bottle first. If baby accepts that, then it’s probably the formula baby doesn’t like. To overcome that, mix small amounts of formula into the breastmilk and feed that with the bottle, gradually increasing the amount of formula while decreasing the proportion of breastmilk. If baby refuses to drink breastmilk from the bottle (try the 3 brands that you have), then it means that baby has a strong preference to your nipple, compared to the bottle teats. I experienced that with both my kids 😅. My second child had the privilege of going for 1 session of milk bottle training with an expert (I didn’t know there was such a thing at first.. haha). Some techniques include holding the bottle with your thumb and index finger (after inserting it into the mouth), then using the other 3 fingers to support the chin and gently lift the jaw (without bending the fingers) towards the bottle to encourage sucking. My LO was a very difficult case 😂 so the Sister had to get her to be very drowsy (keep as upright as possible) before she was willing to suck from the bottle. Unfortunately it’s quite to describe the techniques by typing like that. Oh, one very important thing is also the teat size. If the teat is not age appropriate and the flow is too slow/fast, the baby will also reject the bottle. My LO still sometimes rejects the bottle, although she’s a lot better now. Takes a lot of patience, and if things still don’t work out, please know that there are people who can help:)
Krystal