AT&T wants to terminate my international unlimited data roaming if I upgrade to Z10

I have been on Unlimited International data plan for last years, but AT&T won't let me continue if I upgrade to Z10. I tried calling 3 times, and went to store twice, but no way. I guess I will be forced to leave AT&T and Blackberry platform. I don't think I should replace Torch with Bold (which does not have the latest technology).
Anyone with similar problem? Or found a solution?

Thanks,

K X