Why?

Early in January we received a letter from our bank that because we had excessive withdrawals from our savings account the bank was required by Federal law to convert the account to a checking account. I contacted the bank (three telephone calls and one in person visit) to find out when the change would take place and what the new account number would be. The savings account was closed on January 13 and I had to meet with a banker to get out new account information. On January 15 I made a sizable deposit to our other checking account at the same bank. Yesterday I received a letter from the bank that was dated January 17 (yes, on a Sunday). The letter dated that because they could not verify my husband's social security number the bank had placed a hold on both of our accounts. The letter also indicated that all checks drawn on the account would be returned unpaid and that we would not be able to withdraw or deposit funds until we provided them with the social security number. So, this past week, the bank has returned all of the checks that I wrote (and the online bill pay). Until late yesterday I had no idea that they needed any information as we have had accounts with this bank for over 10 years(and provided them with driver's license and such when we opened the original savings account which they recently closed). So...can our bank simply place a hold on the account without prior warning?