COBOL does not allow data names to differ only by case, but you can distinguish an instance or static field from a method local variable or parameter by using the self:: prefix like this:
working-storage section.
01 PolicyNumber String property no set.
method-id New.
procedure division using by value PolicyNumber as String.
Set self::PolicyNumber to PolicyNumber.
end method.
If you really want two properties (or public fields to differ only by case, you could use the AS phrase:
01 PolicyNumber String property no set .
01 PolicyNumber2 String property no set as "policyNumber".
...but I can't really think of any reasons one might want to do this...