I'll have applied all instructions, but in the date time, when date 2015-07-07 until 2015-10-07, i have change with code =df_reason_mod['Date']=pd.to_datetime(df_reason_mod['Date'], format = '%d/%m/%Y'), the order of the date not change.

Hi Lydia! Thanks for reaching out. Actually, this is the code you should use. So, everything is fine. Could you please share with us a screenshot of your Jupyter Notebook? This can help us assist you better. Thank you. Looking forward to your answer. Best, Tsvetelin