8weeks old not finishing feed

Hi fellow mummies, My 8 week old has not been finishing his bottle feeds recently. He was doing about 110ml and recently he takes 20-30min to finish 60-70ml then starts to fidget and use his tongue to push out the bottle teat. We have tried to burp him and RE-feed but he simply just pushes the teat out with his tongue again and just wants to play/sleep. He then gets hungry again at about 1hr later to complete the remaining 40-50ml. The time difference between each feed is about 3.5-4hour for each fresh bottle we give him. Any tips/advices to help him finish his milk at one seating? Ps: we have tried changing to a faster flowing teat but no success at all Thanks in advance