now, I am worried if the data will be misused. Any suggestions? should i disable my card and request a new one? or am being paranoid? do CSR of reputed organizations do such things?
The first thing you should do is call your bank and ask them about the rejection. If the CSR legitimately tried to run the card and had it declined, they can see that and tell you why - and if they can't find any record of it, you can cancel the card right then... but you still may not have to.
There's obviously no way to be sure that the rep didn't write down your card information for his personal use later, but any company that does MOTO (Mail Order/Telephone Order) transactions will have policies and procedures to prevent it, because it's a known risk to their business. It doesn't mean it can't happen, but asking for this information is not immediate cause for suspicion. This reddit thread mentions some examples of the kinds of precautions a reputable business can take to prevent this kind of thing from happening.
Additionally, even if the rep were to write down your information, why would they fake a decline from your bank? Better to write it down, let the transaction go through to ensure that you're giving them legitimate card information, and only then go off to use it fraudulently.
All-in-all, confirm with your bank, but you're probably safe.