The single bay My Cloud unit does not have a recycle bin/trash bin option or feature, that is generally reserved for the multi bay My Cloud models.
Are you using WD Sync?
If so there are a number of complaints about WD Sync filling the free space of the My Cloud hard drive. What happens is WD Sync uses a hidden folder (.WDSyncHistory) to store synced files in case the user deletes a sync file. It allows the user to recover the file or to recover older versions of the file.
There are various discussions of trying to clean out hidden WD SYnc files/folders on a full My Cloud. Here is one such discussion. More can be found using the forum search feature (magnifying glass icon upper right).
