Kaution Problem

The Kaution (security deposit) of a rental contract must be repaid by the landlord within sthree or six (I forgot) moths after the flat has been vacated., minus any damages, outstanding rent or utility payments.
Since you said your flat mate does not return it:
- if your flat mate was the main tenant and you his subtenant, then the above applies and you can ask the deposit back from him, if need be through the courts.
- if you had a joint tenancy, the deposit is with the landlord and not your flat mate, so you should contact the landlord after the joint tenancy ended). (Note: If only you moved out and the flat mate is still in the flat, you generally cannot get your part of the deposit back before he moves out, too!)