Airtel introduced Double Data Offer which valid for 30 days to raise the competition amidst others, however selected customers are only eligible for this subscription you can give it a try
HOW TO SUBSCRIBE FOR AIRTEL DOUBLE
To subscribe for 3GB for N1000,
simply dial *496#
To subscribe for 7GB for N2000,
simply dial *437#
To subscribe for 18GB for N4000,
simply dial *438*1# .