SunTrust Bank Bank Account Or Service Complaint

SunTrust Bank Bank account or service department,

Checking account Account opening, closing, or management Florida

My fianc and I opened a joint checking account at Suntrust bank and deposited a check in the amount of $15000.00. The account was opened on a Thursday and we were told the funds from the check would be available on Monday. On Tuesday morning the funds were not available and the account information vanished from online access. We went to the bank and were told that Suntrust closed the account citing fraud as my fianc owed them money from 2005. After a lengthily process at the bank where we spent time on the phone making payment arrangements for an $800.00 debt we were unaware existed we still are no better off and were just told our funds could be held for 30 days. This has put my family in a very difficult situation. I do n't understand how the bank can legally refuse to return our funds? Please help me understand.