MembershipUser.ChangePassword Rollback when exception - vb.net

Question

I have implemented the changepassword control and am trying to update password in codebehind. It works! But, when testing negative scenario like giving a password less than the required length, the ChangePassword method throws ArgumentException which is ok but at the same time it updates password in the database.
How can I rollback properly? What are the events fired before throwing the exceptions?
Try
Dim password As String = ChangePwd.NewPassword
'update passwordformat
sp.UpdatePasswordFormat(username, "1")
stepsDone += 1
Dim mu As MembershipUser = Membership.Providers("VLSqlMembershipProvider").GetUser(username, False)
'Dim resetPassword As String = mu.ResetPassword()
' returns false if the current password is invalid)
If (mu.ChangePassword(mu.ResetPassword(), password)) Then
stepsDone += 1
'update account to issecurelyupgraded = 1
sp.UpdateUserSecurelyUpgradedFlag(username)
stepsDone += 1
'Else
'sp.UpdatePasswordFormat(username, "0")
End If
Catch argsex As ArgumentException
sp.UpdatePasswordFormat(username, "0")
Catch ex As Exception
If stepsDone = 1 Then
'roll back updatepasswordformat
sp.UpdatePasswordFormat(username, "0")
ElseIf stepsDone = 2 Then
'roll back first 2 steps
End If
End Try
Some Context
I am migrating from clear to hashed passwordformat and have a custom hash implementation.
<membership defaultProvider="VLSqlMembershipProvider" hashAlgorithmType="customhash">
This is why I am first updating password format from 0 to 1, then updating password and in the end setting my dirty flag to false.