As a long time freeze user, it seems literally every time I go to unfreeze the process has changed at one of them and it can't be unlocked with the username +password I setup. The last time was because I didn't log in for 3 years, meant that the account was locked without a bunch of additional validation. Sometimes the validation is just knowing the usual historical address/etc info they ask when you initially set it up (which seems insecure itself), or its more involved.

So, give it time, when you least expect it, they will take 60 days to validate something about your account before allowing you to unfreeze it.