How are you adding the storage? Are you using the `gcloud` CLI or the GCP Console? If you are following specific documentation, can you share it here and I am more than happy to advise you?
If you are using the `gcloud` CLI it might be failing silently so to help identify what might be happening. By adding some debug switches to the command, the output should provide more detailed information about what is happening.
```
$ gcloud sql instances patch <instance-name> --storage-size=250 --log-http --verbosity=debug
```