If you subscribed to airtel BIS lately and you checked your data balance only to see 10MB only after being charged 1500, dont panic you still have your 2GB intact.
Airtel recently changed the code for checking BIS data balance normally you will see your BIS data balance via dialing *141*712*0# but now this will only show the normal data balance and not BIS data balance.
I really dont know why they didnt communicate the changes to their subscribers, the new code to check your data balance for BIS is *123*9#.
Note also the Airtel BIS Plan that gives 2Gb data for 1500 Naira is still working very well on all devices so forget about all the rumors that it has been stopped.
You can read here on how to subscribe to the plan https://wasconet.com/how-to-get-4gb-data-plan-for-n1500-on-airtel-for-2-months/