I had the same issue. The agent claimed no A availability and pulled a joker. Another agent later confirmed to me that there was (still) A availability. Basically, I lost a joker over this. The second agent told me I could escalate it but it would get the original agent in trouble. I didn't want that so I did nothing about it. Then, the original agent called me back and still claimed there had been no A availability, but made me some kind of offer where I would have had to pay Avios or something. He was clearly trying to cover up his own mistake. I just said forget it, no worries. But in hindsight, it annoys me what the original agent pulled off.