data_grouped = calls_grouped.join(internet_grouped, messages_grouped, on=['user_id', 'month'])
data_grouped

-------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-90-0125959be54a> in <module>
----> 1 data_grouped = calls_grouped.join(internet_grouped, messages_grouped, on=['user_id', 'month'])
      2 data_grouped

TypeError: join() got multiple values for argument 'on'