I need to create 1 report with meeting and call activities. 

If you are looking for something the Users can rely on to see a timeline for a particular Contact/Lead the Historical Summary can help with that.

https://support.sugarcrm.com/Knowledge_Base/User_Interface/Historical_Summary_vs._Activity_Stream_vs._Change_Log/#Historical_Summary

If you are on a version higher than Professional and have access to SQL based reports you should also be able to create a rather simple query to retrieve the data you need for a report that might include calls and meetings spanning multiple parent records.

Remember that Calls and Meetings are related via FlexRelate so some may be related to Contacts while others to Opportunities, so regardless of your approach, finding all the Calls/Meetings related to a person/ Account may turn out to be a bit more challenging.

Change Log along with Activity stream-generated  links provide physical data changes that undoubtfully reveal the database relations changes and data changes -however, those are hard to call the business-valuable events, to be aware of which is crucial for getting a 360-degree view on customer relations

An SQL-based report could be a solution for those who know SQL, but (IMHO) CRM users would rather prefer flexible filters, list views, and dashlets of the modern CRM.

Users also hardly interested in technical peculiarities of the platform that allows relating activity either to Account or Opportunity - this should be addressed ASAP for them - for the sake of CRM users adoption

Give a TimeLine Viewer addon a try, to clarify how the TimeLine arranged in Sugar helps CRM users.

Change Log along with Activity stream-generated  links provide physical data changes that undoubtfully reveal the database relations changes and data changes -however, those are hard to call the business-valuable events, to be aware of which is crucial for getting a 360-degree view on customer relations

An SQL-based report could be a solution for those who know SQL, but (IMHO) CRM users would rather prefer flexible filters, list views, and dashlets of the modern CRM.

Users also hardly interested in technical peculiarities of the platform that allows relating activity either to Account or Opportunity - this should be addressed ASAP for them - for the sake of CRM users adoption

Give a TimeLine Viewer addon a try, to clarify how the TimeLine arranged in Sugar helps CRM users.