The baby doesn't want to breastfeed at all. He was initially fed only…

The baby doesn't want to breastfeed at all. He was initially fed only by breast, with inserts, then without them, then there was a lack of weight gain. The doctor prescribed formula and everything, but the baby stopped eating on time. He only took it around sleep, now he doesn't take it even around sleep or during wakefulness. Who has encountered such problems, who can suggest how to return breastfeeding? I really don't want to give up, but I know that pumping is temporary (the milk production will not be sufficient).