Could you please make it clear if you want to Block File Sharing from Symantec Firewall or any other source?
Also if you check the Firewall Settings in the Symantec Endpoint Protection Manager Console the File Sharing is already blocked.
1. Open the "Symantec Endpoint Protection Manager"
2. Click on Policies
3. Click on Firewall
4. Select Edit
5. Click Rules on the Left side
6. Rule Number 8 which is unchecked shows that Firewall rule is set to be Blocked
7. Put a check mark Next to this rule to enable it.
8 Click Ok
You can check if this rule is assigned to a Group and then check File Sharing and Printer Sharing.
I would suggest you to create Test Group and assign this Rule to that Group and Move a computer into this. Then test the Rule.