Hi Samuel
My understanding is that you already tried to increase the disk space [0][1][2][3] in the instance and you do not have access at all.
Please sent me via a private message your Project ID and your instance name, as well as any error you are receiving.
[0] https://cloud.google.com/sql/docs/mysql/edit-instance
[1] https://cloud.google.com/sql/faq#storage_limits
[2] https://cloud.google.com/sql/docs/mysql/diagnose-issues#disk-space
[3] https://cloud.google.com/sdk/gcloud/reference/sql/instances/patch