Bugged mobs are breaking my server

There was a bug with one of my spawns that caused it to spawn literally 1000 - 4000 of these birds into a small space. I am not sure what caused it but I've removed the birds. the issue is that now the remaining ones that I tried to mm mobs killall before restarting but apparently they lived, these remaining birds are bugged. /killall doesnt do it /killall Parrot doesnt do it, /killall all doesnt do it and /mm mobs killall doesnt do it.

They are breaking the server because so many spawned...

Bugged mobs are breaking my server