MTN lies about there Roaming. They have No Roaming partner in US!

I am currently Houston/United States ans MTN ROAMING sucks. My roaming was activated before i left SA. Now there is no way to Roam. i have tried Manual network registration and automatic. Both method doesn't work. So what now? You have only partner in US? Manual network shows At&t is your partner. others are Forbidden for MTN sim. Please help so i can use my MTN sim. Urgent help please.