I never heard of a frozen account, but my 2 cents are that there isn't much you can do.
My number was banned from Telegram for no reason (and when I mean no reason, I actually mean no reason, it was a brand new account and I hadn't even messaged anyone, I did join channels, but they were only channels validated by Telegram, so that couldn't have been the reason).
I sent them emails to try to get my account unbanned, but it was useless, they never did anything.
In the end, I was lucky enough that I configured my account to autodelete by 6 months, which ended up happening and I could create a new account after waiting. So the ban is linked to the account, not the number.
By default I believe the wait time is a year.
Now I've actually been using it a bit more, messaging some friends, connected through my VPN, and sometimes even changing countries multiple times a day between America and Europe when I have poor internet. Never got banned again.
It makes no sense, but after reading similar stories on Reddit, the general consensus is that they banned many people for no reason, and there's usually nothing you can do other than wait.