My mum once gave the right answer as the “phone a friend” on who wants to be a millionaire.
She was given some money as a thank you - I have a vague recollection that it was £500. She was happy with this although other people felt she should have been given more (person didn’t become a millionaire but they did win a decent amount).
I used to know a man who was very hot on money and getting what he considered his fair due. He always said that, if he were called as a Phone A Friend and he knew the answer for sure, he would spend the first few seconds striking a deal as to how much he would of the increase in prize money he would get as a direct result of his answer, before giving it! It sounds kind of cut-throat, but thinking about it, I don't really blame him.
They haven’t thanked you because they have no intention of giving you anything.
To thank you, would be to acknowledge your contribution, and they haven’t because they don’t want to share.
Yes, I was thinking exactly the same. Unless they're the unpleasant kind of person who never says thank you if you hold the door for them or pass them something, that's definitely their thinking. If you pushed it and asked for a share, I wouldn't be surprised if they claimed they knew the answer anyway and you 'forced' it on them a nanosecond before they remembered it. They've calculated this carefully and happily used you before deliberately dumping you like a hot turd.
I'm not suggesting that this is what should happen, but I think there's potentially a moral case to treat this that OP was the prize winner - i.e. giving the correct answer that brought in the £12K - and the colleague was OP's 'agent' in setting up and being an (albeit accidental) middleman linking the source of the potential income and the 'work' needed to earn/win it. Therefore, the majority was 'earned' by OP, who should thus get the majority of it, and the colleague should have had 10-15% of it, or whatever the standard agent's fee is!!