July ACT cancelled but not allow to change test center

We got email last evening that my son’s July ACT test was cancelled, and it also said we can try to change to a different testing center “ACT has extended the deadline for you to be able to make this change to July 1.”
But on ACT website there is no way to change center, and ACT phone number is always busy, any suggestion please?

Unfortunately, I think you’re going to have to keep calling.

I had to keep trying every hour or so, and then poof! I was able to see available sites. Good luck!