Where Do I find my calls logs?
For Android:
1. Tap on the Chat menu icon 
on top right side corner.
2. Choose a conversation from your Recent Chat conversations that have notification
3. You will see missed call in Chat thread.
As a Caller:
As a Called user:
For iOS:
This feature only available for Android users, and soon will rollout for IOS users in next incoming updates.
Note: Currently you will receive i missed call notification for iOS users only if someone called you.