import pandas as pd

wb = Workbook()
ws = wb.active

df_data = {
           'year_month': ['2019-06', '2019-06', '2019-06', '2019-06', '2019-06',],
           'lead_source': ['C', 'IH', 'INH', 'INH', 'MV'],
           'status': ['Lead', 'Lead', 'Lead', 'Refund', 'Lead'],
           'leads': [12, 7, 51, 2, 15],
           'total': [140, 280, 918, 36, 150]
           }
df = pd.DataFrame(df_data)

# Does work
try:
    ws['A1'] = df[(df['lead_source'] == 'C') & (df['status'] == 'Refund')].iloc[0]['total']
except IndexError:
    ws['A1'] = ''

# Doesn't work
def cell_insert(cell, data):
    try:
        ws[cell] = data
    except IndexError:
        ws[cell] = ''

cell_insert('A2', df[(df['lead_source'] == 'C') & (df['status'] == 'Refund')].iloc[0]['total'])

wb.save(r"stackoverflow.xlsx")