To clear the cache for New Microsoft Teams:
C:\Users\user.name\AppData\Local\Packages\MSTeams_8wekyb3d8bbwe and delete the whole folder
Tip: to find the AppData folder you will need to go to View > Show > Hidden Items
...
To clear old Team cache:
C:\Users\user.name\AppData\Roaming\Microsoft\Teams and delete the whole folder