This happens when special characters are not treated specially, for special character we should use UTF-8 encoding rather then ASCII.
SQL Server Reporting service there are option of Html and csv (download).
byte result = null;
string format = @"CSV";
string devInfo = null;
string streamIDs = null;
string historyID = null;
Warning warnings = null;
ParameterValue reportParameters = null;
ReportData reportData = null;
1) line to be updated
devInfo = @"
rather than following.....
2) reportData.ReportOutData = Encoding.UTF8.GetString(result);
3) //Save CSV if (its csv)
File.WriteAllText(file, header+Output, Encoding.UTF8);
//header because in devInfo we have set it to NoHeader, so manually we need to set it.
it will sure resolve the issue
Comment if it resolve/not-resolve the issue