Grouping already clustered data (with a pre-defined x and y)
It would be helpful to know which clustering technique are you using.

You can use


Partition-based Clustering: for example K-Means Clustering, not that good with outliers.
Hierarchical-based Clustering: Produces trees of clusters (Agglomerative, Divisive). You get a Dendogram.
Density-based Clustering: produces arbitrary shaped clusters, for example DBSCAN


If you are looking something other that a circular cluster and you need clusters within clusters, I would try DBSCAN. It locates regions of high density and separate outliers and it can find clusters within clusters.

If you are using Python you can use DBSCAN with sklearn

from sklearn.cluster import DBSCAN 


I hope that helps!