It looks like have only allocated 500 GB of storage to your node which is why the available is <0 and the used is 500 GB. Therefore the storagenode will not get any more data.
The storage allocated is set when you create the storage node in docker. Have a look at: https://github.com/storj/storj/wiki/Explorer-Release-Setup-Instructions
The default value is -e STORAGE="2TB" \
You can change this value by running:
docker stop storagenode
docker rm storagenode
then recreate the storage node as the same way you did before with a different storage value using the docker run command.