Vodacom unable to route International

In December 2015, I ported my phone from MTN to Vodacom. Since that time I have been unable to receive international calls from some locations to my phone. The person calling is told the the phone is not on the MTN network. All works well within SA and while I am travelling my phone works, although my international roaming was terminated two weeks ago. <br> So months later, I am still unable to receive calls from persons abroad and Vodacom is unable to resolve this issue.