If you want to block a caller from calling any numbers on your account, please follow the below steps...
1. Login to selfcare
2. Browse to Reports -> Call Detail Records
3. Load the call records for the period you received the call.
4. Find the call record in the list, and using your mouse, hover the cursor over the CLI field.
5. An option should appear, which says Block Caller. If you click on this, that number will be blocked from calling you in the future.
6. If you want to unblock the number, simply repeat the procedure.
A video guide for the feature is available below...