I just found out that MTN has been giving free airtime as rewards to their customers (but only for their music customers) But you can do some little tweaking to get the free airtime as a normal user with the following steps :
Step 1: Download and install Music Plus APP on Google Play Store by searching “Music Plus” Or visit http://musicplus.mtnonline.com to download and install Music Plus APP
Step 2: Login with your mtn number and Subscribe to a 30 Days Plan
After Subscribing successfully, you will get 500 bonus points automatically (note that even with little or zero airtime balance you can still do this successfully)
Step 3: Text stop to 5900 to unsubscribe
Step 4: Subscribe and Unsubscribe continuously
You get 500 bonus points every time you subscribe (You can convert these bonus points to mtn airtime and claim at any time you want on Music Plus APP)

Just like that you can get FREE MTN Airtime!!! every day like I have been getting for the past 4 days now. However You will be blacklisted on the platform if you constantly subscribe and unsubscribe, but don't worry, because the next day you can continue again. Good luck and remember to send my share

I tested and it works,