Group iMessage spam with hidden sender cannot be blocked

Recently I have received a few imessage spams that have the following characteristics:

1. they are send as group messages, i.e. there are two senders.
2. one of the senders has a phone number, while the other one DOES NOT HAVE ANY PHONE NUMBER NOR EMAIL ADDRESS.
3. the phone number can be blocked, but the hidden sender can not be blocked.
4. Message app does not show a "report junk" link for this kind of message.

A example of such a spam:

one sender has a phone number +855319610958 , the other sender has a name "🌅澳门新葡京赌场招聘代理" but does not have a phone number or email address.