How to block LINE stamp spam

Question

In the Android app LINE, since yesterday, I started receiving spam messages like this one (below the advertisment):

The spammer (with the name "LINEスタンプ" in this case) appears in my messages list despite not being my friend.

I have deleted the conversation, but more messages have kept coming yesterday and today.

Is there any way to block or report the spammer?

• I would rather not open the message.
• The long-press menu does not show any block option, only "Delete" which I tried already.

Answer 1

The "LINEスタンプ" account is automatically added (with your permission nor knowledge) to your friends (in the "Official accounts" tab) when you download any stamp collection:

Long-press it and select "block":

Then delete the conversation. It should not reappear this time.