When you block a user in the Message Centre, you will no longer receive message from the person.
To block a user, click the sub-menu on the top-right corner of the chat. Click “Block”.
To unblock a person, click the sub-menu on the top-right corner of the chat. Click “Unblock”.
If a user is marked as having “abnormal activities”, the user may be categorized as a spammer since abnormal activities are detected in the account. The chat will be under restriction. You will not be able to receive any message from the person.