Our checking account has been "garnished" by a credit card ! Most of the money was my Social Security..?

It is true that Social Security benefits cannot be garnished. However, when you mingle those funds with other funds in one account, the bank has no way of knowing what is what. You'll need to set up a separate account for Social Security benefits ONLY and have them deposited there. When you do that, go see your bank and make sure that they flag that new account accordingly so it is not garnished.