IOS – On iOS how can I add an alphanumeric sender ID to a contact

On my iPhone I like to have a contact associated with any number from whom I receive messages. However, I've been struggling to do this with texts from (e.g.) my bank who use an alphabetic sender ID. I've tried adding the text that appears in the Messages app to the contact as a mobile phone "number" — the Contacts app accepts this, but it doesn't get associated with the contact in the Messages app.

Does anyone know how to do this? These textual sender IDs are quite common these days so it would seem like an obvious thing to support.

I have an iPhone 6S running iOS 10.

EDIT [2016-09-17]

It appears from the comments this may be a region-specific feature – to clarify, I'm in the UK, so it's quite possible we're not a large enough market for them to bother about supporting these more gracefully.

Here's a snippet from my Messages screen – note that these are not contacts, this is how the SMS arrives even if it's from a totally new sender:

If you try to add to existing contact, it doesn't add anything.