How incredibly frustrating for the OP. It’s one thing for agents to make a genuine mistake (and we all have bad days), but you do wonder whether someone with this mindset and blinkered approach should be allowed any direct contact with customers.

That quote in the thread title took me back over twenty years to the surreal press conferences held by Iraq’s Minister for Information.
The BA phone agent’s truly bizarre line of defence - “Our systems never have issues” - has to be right up there with the many infamous claims made by the Minister, who soon came to be widely known as Comical Ali.