How not to show/dipslay an index in csv when adding a new row using python pandas

I have a CSV file that I used to get its values from a columns but my problem is the value I'm getting is from the two headers which is Rounded-Download-Speed and Rounded-Upload-Speed so what I did is separate them and concatenate it.

Then I'm adding a two row to separate them inside but the problem is the index of the row displays but what I want for that is to be a blank cell. Here's my code:

import pandas as pd
from decimal import Decimal, ROUND_HALF_UP

L=['0000','0100','0200','0300','0400','0500','0600'
                                        ,'0700','0800','0900','1000','1100','1200','1300'
                                        ,'1400','1500','1600','1700','1800','1900','2000'
                                        ,'2100','2200','2300']

df1 = pd.read_csv('Sample.csv')
df1.Date = pd.to_datetime(df1.Date, dayfirst=True)
df1 = df1.pivot_table(values='Rounded-Download-Speed',index='Date',columns='HourBin',aggfunc='max',fill_value="ND")
df1.columns = df1.columns.astype(str).str.zfill(4)
df1.index = df1.index.map(lambda t: t.strftime('%Y-%m-%d'))
df1 = df1.reindex_axis(L, axis=1)
spaceRow1 = "-"
df1.loc[len(df1)] = spaceRow1
spaceRow2 = L
df1.loc[len(df1)] = spaceRow2

df2 = pd.read_csv('Sample.csv')
df2.Date = pd.to_datetime(df2.Date, dayfirst=True)
df2 = df2.pivot_table(values='Rounded-Upload-Speed',index='Date',columns='HourBin',aggfunc='max',fill_value="ND")
df2.columns = df2.columns.astype(str).str.zfill(4)
df2.index = df2.index.map(lambda t: t.strftime('%Y-%m-%d'))
df2 = df2.reindex_axis(L, axis=1)


df3 = pd.concat([
    pd.concat([df1], axis = 1),
    pd.concat([df2], axis = 1)]).to_csv("Output.csv", header = True, encoding = 'utf-8')

Here's the output, the index is the date:

            0   100 200 300
05/03/2017  ND  ND  ND  ND
06/03/2017  ND  ND  ND  ND
07/03/2017  36  36.2    36.2    21.3
08/03/2017  35.5    35.5    59.8    35.9
09/03/2017  35.7    43.6    35.2    35.2
10/03/2017  ND  ND  ND  ND
         6  -   -   -   -
         7  0   100 200 300
05/03/2017  ND  ND  ND  ND
06/03/2017  ND  ND  ND  ND
07/03/2017  1.4 0.2 0.3 0.3

I want the index 6 & 7 to be empty just like the index 0. But I can't figure how it's not working like the index 0.