Mickchick,
I'm sorry to hear that you didn't get the seats you would've liked. I'm even more sorry that you encountered the Purser on your flight. Not only was he lying to you (see post above), but he obviously had no interest in your situation at all.
When a passenger comes to me and explains the situation, whether it's medical or something else, like small kids, and that they're not seated together, I will do my ultimate best to fix it. Fortunately a vast majority of crew will do the same. It's such a shame people like that Purser give the rest of us a bad name.
May I ask: Did you manage to swap with another passenger at all?
Gg