How to block LINE stamp spam

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, can also be LINEで応募) 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.