Thanks to Daniel Dieb, I fixed my problem. He commented on a similar
post:

If ForRendering has a value of false, the parameter meta data returned
represents the parameter data that is currently associated with the
specified report. If any parameters values are based on a query and you
are
interested in returning the query-based parameters valid values list,
you
need to set ForRendering to true, In addition, for query based
parameters,
you need to ensure that you have passed in all of the credential
information
required to return the query parameters.
I set this parm to true and got my values!!