Freezing a corporate bank account for unknown source of funds

Hello,

I am the manager of a travel agency, and we have a bank account with one of the big banks.

I was surprised last month that the account was closed without informing me, and when I contacted them, they told me that the source of the money entering this account is unknown.

The problem is still not sorted until now, and I am contacting them on daily basis without avail.

Please let me know, what should I do? This is causing us a hassle at work let alone damaging our reputation in front of the people we are dealing with.

Thank you.