Try to increase your credit limit on Apay card (by requesting customer care). Once that is done, re-apply in December end via same C2C method.
The issue with co-branded cards is that they are difficult to upgrade (that's what I have heard) and so, I won't suggest PayTM-HDFC CC if you are not going to use PayTM exclusively (as it also has monthly fee)
Wait and apply for Millennia, at least there would be a hope that you might get upgrade offers to Regalia or DC Privilege in future.
Suggestion: Don't do it via call agents, the process is extremely slow with risk of sharing documents over mail/whatsapp. Goto bank and ask the CC team if they Unconditional LTF form at end of quarter like last week of December (that would a plus for you)