How can I block messages received in a 5 digit number?

Hello pattinay,

Thanks for posting in the Apple Support Communities. We're happy to look into this with you. You would use the same process blocking these like you'd block a contact with a full phone number. If you're not sure of the process, check out Block, filter, and report messages on iPhone - Apple Support for full details.

Block messages from a specific person or number

1. In a Messages conversation, tap the name or number at the top of the conversation.

2. Tap the  info button, scroll down, then tap Block this Caller.

To view and manage your list of blocked contacts and phone numbers, go to Settings  > Messages > Blocked Contacts. See the Apple Support article Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch.

Best regards.

Those are short code messages. Forward them to 7726 (SPAM) for your carrier to deal with.