SQL类条件不能显示我的搜索数据c#和Ms Access

我尝试通过MS Access (SELECT mname, mcellno WHERE mcellno LIKE '0922*')进行查询，结果显示我想要的数据。而这个

    private Int32 getMemberNo()
    {
        con.ConnectionString = db.konek();
        String sql = "SELECT COUNT(*) AS x FROM members";
        Int32 count = 0;
        try
        {
            con.Open();
            OleDbCommand cmd = new OleDbCommand(sql, con);
            OleDbDataReader rdr = cmd.ExecuteReader();
            if (rdr.Read())
            {
                count = Convert.ToInt32(rdr["x"].ToString());
            }
        }
        catch (Exception ex)
        {
            Console.WriteLine("Error: " + ex);
        }
        finally
        {
            con.Close();
        }
        return count;
    }
    public String[,] displayMobilePrefix() //THIS FUNCTION
    {
        con.ConnectionString = db.konek();
        String sql = "SELECT mname, mcellno FROM members WHERE mcellno LIKE '" + @mcellno + "*'";
        int count = this.getMemberNo();
        String[,] ars = new String[2, count];
        try
        {
            con.Open();
            OleDbCommand cmd = new OleDbCommand(sql, con);
            cmd.Parameters.Add("@mcellno", OleDbType.VarChar, 30).Value = this.mcellno;
            OleDbDataReader rdr = cmd.ExecuteReader();
            int counter = 0;
            while (rdr.Read())
            {
                ars[0, counter] = rdr["mname"].ToString();
                ars[1, counter] = rdr["mcellno"].ToString();
                counter++;
            }
        }
        finally
        {
            con.Close();
        }
        return ars; //never returns any data
    }

它不会返回任何数据。然而，我试图在我的字符串查询上添加一个参数，它什么也不返回。

String sql = "SELECT mname, mcellno FROM members WHERE mcellno LIKE '" + @mcellno + "%'";