Birds getting into fruit cage

Simple, theres a hole. Somewhere. I have a similar problem with small birds getting into my covered chicken enclosure. Theres a small hole about 2 inch diameter where the top of the coop has rubbed the netting.

Thrushes eat snails and usually have an 'anvil' somewhere in the garden - ie a rock they break the snails shells on. Its quite likely the hole is low to the ground where you havent seen it, look for a rock nearby with snail shells on it and if you find one loook at the netting closest to that rock

The only way to stop them wanting to go in for the fruit is to not grow fruit!