What needs to be done to end date a benefit plan?

Summary

Attempting to end date a medical plan for upcoming year.

Content

We are preparing for open enrollment for 2020 benefits. The only change needed is to remove one Medical plan option. I have made the plan inactive as of 12/31/2019, but receive an error stating "You cannot delete a parent record when child records exist. (BEN-990391)" when attempting to end date at the program level. 

Subsequently I have end dated the plan options at the plan level. Then attempted to end date the rates associated with the plan, but received the same error. Is this due to current enrollments in the plan? Any guidance would be appreciated!