You can call from your mom phone and call tmobile then tell them that you need then to unlock it.
What Do I Do If I Forgot My Tmobile Phone Pin?
Go to t-mobile and they'll tell you the same thing happened to me. They had to unlock my phone bc the sim card blocked itself.
You can do what you did wen you changd it because I had 2 do the same thing it was hard but I got it. If that don't work call custome service and thet unblock it for you so give it a 100% rite anwer