First, I want to say for the benefit of anyone reading, that if you have any instinct about the situation,
listen to your gut.
...I registered the domain some years ago but i don`t need $xxx. This company is spending a lot on this project and I think they could afford much more than $xxx. I would be sad after selling them my domain for less than $xxxx and I will ask them $xxxx. If they won't negotiate i will keep it.
Thank you so much Chris.
From our conversation, they are acting irritated with you. They are basically trying to force the issue. As if there is nowhere else to go from here.
If they are truly irritated (offering 23% of what you want), then pushing your full asking price will just get them more irritated. Instead, you
could say:
"Thank you for your kind offer. Unfortunately, our figures are too far apart. I strive to conduct business in such a way, that everyone would leave the table happy. And, I would never want you to get in trouble with your CEO. Best of luck in finding a nice domain at your desired price point."
I suspect they are only
acting irritated. It strikes me as a well-calculated stance that may have worked quite well in previous negotiations. If that is the case, the above response would serve you just as well.
The best tool in a negotiation is the willingness to walk away. You have that, so it may time to be abundantly clear about that.