Use a new sim for better result or a Mtn sim that hasnt been given the 750mb
Tweak this IMEI number on your phone 352373058168932 for 750MB IMEI
Now after tweaking it, just send smart to 131 and wait for the response from MTN.
Tweak this number 359757053317082 for 300MB IMEI and after that, Send Mifi to 131 and wait for the response also.
Tweak the last fifth digit
Normally, when it is successful, you will get a message that the data has been given to you. Anyway, you can also check the data by dialing *559# or ***559*4#
It last for 3 months.
Dont forget to comment if you get yours