Here's the message they posted -
Pick up that MTN sim you haven't used for 30days or more and enjoy this great offer. Get 1GB for N200, Dial *131*65# to enjoy!! What are you waiting for. #MTNWelcomeBack
So basically this is a welcome back plan
How To Get MTN 1GB For N200
Simply get an MTN Sim that you haven't used for 30 days - 180 days.
Load N200 naira on the Sim
Then dial *131*65# to buy 1GB for N200
Data is valid for 7 days.
To check Sim eligiblity, dial *559*65#.