How to block SMS from short code / sender ID like "XY-ABCD"?

I've been receiving SMS from a social organisation I was once associated with. The organisation keeps on sending their promotional / event messages on my phone via their short-code or sender ID which is in the format XY-ABCD. When I try to add number to 'spam numbers' on my mobile; I get 'invalid phone number' message. That's obvious because there is no phone number associated with that ID!

There's no other option to block the ID from sending messages to my phone; and I'm wondering if there's anything I can do about it. I've contacted the organisation but they aren't helpful.

Does anyone know how to block such codes / IDs?