Banks typically block accounts when they suspect fraudulent activity. This can happen if there are sudden, large changes in account activity, such as a large number of withdrawals or transfers. Banks may also block an account if the account holder has been reported for fraud in the past.
If you think your bank has blocked your account, the first thing you should do is contact customer service. They will be able to tell you why your account has been blocked and what you can do to fix the problem. In most cases, you will just need to provide some additional information or documentation to prove your identity.