[Q] Nokia Lumia 521 internet sharing problem topic

I recently bought a cheap Tmobile US Nokia Lumia 521 for on a retail store and I activate a prepaid number from tmobile and i used tethering without a problem; now i switched to my original sim card from Simple Mobile and I tried to use the internet sharing app from the nokia and didnt work with simple mobile and have the correct apn every time I tried to activate the built in app I receive this error: Conection Not shared internet sharing isnt currently available but i switch again to my tmobile sim and works fine. Any fix for this problem? Any app for tethering? Btw i have a tmobile usa HTC HD2 with andrid and works fine the tethering with the jelly bean built in app