Why wont my chickens lay?

I’ve had my 4 chickens over a month and they were at point of lay when I got them from a local farm.They are now 22 weeks and still no eggs. They are fed laying pellets, corn and mixed greens, I let them out at 6am and house them at 8pm plus they are free to walk around the garden for most of the day so they eat worms and bugs, so they have plenty of room to exercise. They all seem to get along well but none have attempted to a single egg.
Is there something i’m doing wrong?
Sorry forgot to mention I can’t have a rooster where I live cause of noise pollution and they are being given oyster shell

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