My phone was stolen How can i block my sim card online as am not close to an MTN store

my date of birth is 26-01-78 and my names are Jonathan idonuan Obaika, a native of Edo State.

I bought a registered sim card from an MTN agents at Ebonyi State,Ohaozara precisely,and it's was blocked recently,I have not been using it for calls all this while,what should...