The suffix -ejo is for places, not for containers. You should not use it for an office cabinet. The suffix -ujo is used for containers.
Where in Vortaro.net did you see that? It's clearly stated it is a container, not a collection. That would be dosieraro.
I looked into the Esperanta Bildvortaro and found slipujo, which makes sense since you don't put files directly into such a cabinet.