Wa'alaikumassalam sayang! Hmm, memang challenging sikit situation ni, especially bila dah tried multiple bottles & teats dah. A few of mum friends aku pernah kena situation macam ni, sometimes it's the teat flow yang tak suit (some babies prefer slower flow, some prefer faster), or dia dah used to breast so susu botol texture/temperature berbeza sikit, or even the bottle smell if it's new brand. Since susu badan dah stop, maybe boleh try warm the formula slightly & jangan force, let him explore the bottle at his own pace, tapi honestly sebab anak cuma 4 bulan & intake susu berkurang, better check dengan pediatrician cepat-cepat to rule out any feeding issues atau if ada other underlying reason dia reject. Sabaran, mama, ini phase saja & doctor can guide you better from sini!