Today I logged into Bittrex to see that my account has almost no balance.

I checked my WITHDRAWAL HISTORY and saw that on 2018/09/04 21:59:06, there was a transaction 1.04294260 btc to address 154S7gFkomrXyABgs1i8XWmAKhUCcfRkcz

There are also 0.01135790 btc to address 154S7gFkomrXyABgs1i8XWmAKhUCcfRkcz on 2018/09/04 22:01:30, and 0.00653546 btc to address 182JPuxQgTzHX8ZSo44SFa32uLLy7qgHqG on 2018/09/06 05:08:08

There are many problems here:
1. I did not have any Bittrex Login Notification email on 2018/09/04 or 2018/09/06 (which mean I did not login or having any actions of login to Bittrex on those time)
2. I still have my 2FA on
3. All of my API keys do not have Withdraw permission
4. I did not have any sessions of using Bittrex on those time
5. My gmail need mobile verification to login, an on those time I did not have to confirm any new location Gmail login
6. I did not change or disable my 2FA for months, until now.

I feel very sad that I logged in to my Bittrex rarely these days, being confident that my F2A will keep my Bittrex safe. I still don't understand how could hackers logged in to my account without 2FA or triggering a notification email, and performed 3 transactions without needing to input my 2FA.

I am very confused right now as my altcoins are bought from low price, and I am holding my bags. I logged in today to refresh my orders, and what I get is an empty account.