Let's not get into name calling, and instead discuss the issue, ok?
Think about it, Tmobile has NOTHING to do with your AT&T phone, it cannot provide you support on something that it has nothing to do with. If the phone is not SIM unlocked, you can only use it with AT&T. Remember, the phone has to be SIM unlocked - only AT&T can help you with this, even Apple can't.
By default, all AT&T phones are SIM locked to AT&T networks. So, unless you received an unlock code from AT&T, and entered it on the phone, it is not unlocked. There are many types of locks, please don't confuse SIM/Carrier lock with any other type of locks.
Would it be possible to post the content of the AT&T email (after hiding sensitive info such as phone #, serial no, account no, etc) here?
Now, if you don't want to deal with Tmo at all, you can simply go to AT&T with your Tmobile account number, and the password that you setup when you created the account, and AT&T will be able to port your number back to them in a few hours, minutes in most cases.