ziggyboy, a few questions ...
What's the norm in
what industry ?
How do you know there's a hiring freeze?
If you have accepted the offer it is a legally binding agreement, so at the very least they would need to terminate your employment and pay you for any notice period. Whether they can do this probably depends upon the wording of your employment agreement.
If they are a large reputable employer and you haven't hear anything I think it's reasonable to assume that there isn't a problem. You could of course ring them up and ask
Have you resigned from another job?