My SIM was stolen, I want to block it, can you people help me block it?

Hi Julius, to block your line, you need to contact any MTN customer care support
find below MTN Nigeria Contact Channels.
1. MyMTN App
2. Facebook: @MTNLoaded
3. Instagram: @MTNNG
4. Live Chat: http://bit.ly/2OC5bHz
5. Email: customercareng@mtn.com
6 .WhatsApp: 09033000001
7. Call: 180