It sounds like you had a prior CPS intervention involving a Petition in court and reunification services. It also sounds like you completed the services successfully and the case was dismissed but you are now slipping or relapsing.
The Department (CPS) will not stop looking at you until they feel confident you are not back into using drugs or alcohol. At some point - they felt you were not taking proper care of your children because of AOD (Alcohol or drug) issues. You need to stay away from these until your children are adults.
This is what you need to do to help close the investigation with social workers.