Better you first mail them along with income documents, if not successful, send physical letter to their Chennai office.... Mine limit was just 87k when they issued me Money Back cc, but now i have 2.36l and also card upgrade from money back to millennia and also i have infinity with same limit. Mine limit was increased when i did heavy txns with the card, also card upgrade came when i utilised 90% limit in just one month in a single txn!!!