Oracle Parametrized Query From Ado.Net

So this is the error I have been getting: ORA-01036: illegal variable name/number

All I am doing is trying to update the table with these values. The values are not null and each of the variables in the parameters have values in them.

The Query executes well in Oracle (without Parameters), but it gives ORA-01036: illegal variable name/number, when I add parameters.

I have tried almost everything, but with no luck !!

using (OracleConnection con = new OracleConnection(cs))
{
const string query = @"UPDATE ASSOCIATED_CENTERS_INFO
SET DIS_ASSOCIATED_BY = (SELECT ID FROM VC_ADMINISTRATORS WHERE USERNAME = ':USER'),
DIS_ASSOCIATION_DATE = SYSDATE,
ACTIVE_YN = 'N',
NOTES = CONCAT(NOTES, '<br>' || SYSDATE || ' ' || (SELECT FIRSTNAME || ',' || LASTNAME FROM VC_ADMINISTRATORS WHERE USERNAME = ':USER') || ': ' || ':COMMENT')
WHERE OSC_ID = :OSCID AND ASSOCIATED_OSC_ID = :ASSOCIATEDOSCID;";
OracleCommand cmd = new OracleCommand(query, con);
cmd.CommandType=CommandType.Text;
cmd.Parameters.AddWithValue(":USER", userName);
cmd.Parameters.AddWithValue(":COMMENT", comment);
cmd.Parameters.AddWithValue(":OSCID", selectedIdOnMap);
cmd.Parameters.AddWithValue(":ASSOCIATEDOSCID", selectedIdOnListBox);
con.Open();
cmd.ExecuteNonQuery();
}