1. Dial *777#
2. Reply with choice 1 for 4G-3G Data Plan
3. Reply with choice 4 for Get Data Balance
4. Reply with choice 4 for Manage Plan
5. You will receive a prompt with your data balance

EXAMPLE
STEP 1
Send:
*777#
Response:
1.4G-3G Data Plan
2.BlackBerry
3.4G LTE Coverage
4.Voice Profile & Plans
5.Super Max Combos
0.Exit

STEP 2
Reply:
1
Response:
All Glo data Plans are now 3G-4G compatible
1.Buy 3G-4G Data Plan
2.Gift Plan
3.Share Plan
4.Manage Plan
5.Back

STEP 3
Reply:
4
Response:
Please select

1.To get Data Settings
2.To see Details for manual Configuration
3.To go to Selfcare Portal
4.Get Data Balance
5.Back

STEP 4
Sent:
4
Response:
Your account is ACTIVE and will expire on 02/10/2017 14:43. You are on N5000.Your remaining volume is 9845 MB.Your renewal status is ACCEPTED.

Source: Glo Data Balance