My account says I'm not verified. But I don't seem to be locked.
I remember they did send an email a while back saying something about locking accounts. I'm pretty sure it was for those who didn't have 2FA.
I also met this case and I think you should talk to them about your problem because COSS has a very good support team and is very professional. At the moment, this is a very low volume and many investors are leaving this exchange for a better exchange. I personally recommend switching to Binance or Bittrex as these are a far better exchange than COSS