I really want the job even if that means waiting 6 months.
So do that. The company informed that they are putting the position on hold, not you or your application. There's nothing much you can do from your side now.
You can respond them by thanking them for the opportunity, something like
"Thanks for allowing me the opportunity to interview with your organization. I'll be looking forward to resume the communication once the position becomes available in future. Thanks."
That being said, I'd not be relying on them to get back, the message you received may very well be a simple rejection message, disguised as the postponing message, to encourage applicants to re-apply after a certain period of time. If you need a change of job, keep looking elsewhere. In case this company contacts you in future, you ca take the call at that point - but if I were you, I would not have relied on them getting back alone.