Oracle using sub-optimal index on bind variables
I would create a composite index on (CUSTOMER_ID, ORDER_DATE) and that should fix all your issues, assuming ORDER_DATE is a DATE data type.  And assuming ORDER_DATE should not be null, ensure the table definition says NOT NULL.  I am certain Oracle is not using "some random value" if you gathered statistics correctly.  You tagged your question with both 11g and 12c; you running different versions on different instances?

Is your bind variable the correct data type for the ORDER_DATE?  If this is a vendor application, you may need to create a function-based index on the ORDER_DATE column to produce a reasonable date that matches the format of the bind variable.