Frozen account is something similar to ban. In case of ban you know how many days it takes, but if you have frozen account it will be active until you solve the reason. And the most common reason of frozen account is unfortunately trying to cheat on payments. For example you bought a premium time, but you canceled your payment. Then Cipsoft freezes your acc untill they get their money.
All you can do is to contact them directly.
If your friend is sure that something went wrong with the payment - just write to cipsoft via email or ticket.
Visit also FAQ > Payments.
If your friend has absolutely no idea what is the reason, maybe it is a bug. History knows situation, when player did some steps in a particular directions in depo thais and he suddenly puffed and his accound became frozen. Just due to a bug.