Go to a branch, works best.
Let me summarize my personal experience.
TATA NEU INFINITY HDFC - Got call from agent offering it LTF.
DCB - applied via Greviance Redressal and customer care, rejected with the reason that Tata Neu was issued and the cooling period of 6 months before new cards can be issued. CC and Greviance Redressal are useless.
Got call from agent offering Regalia and Regalia Gold both LTF, told not interested but interested in DCB under Alumni offer. Agent took permission to skip the cooling period and applied, got approved.
I repeat sales team has a lot of leeway, customer care does not. New customers (sales) are valued more than existing ones (CC).
And don't have agent numbers, never thought of keeping it as I get once a week calls from HDFC still now.