Would charges for late payment of  dues on credit card outstanding be  chargeable to GST?

Yes. The exemption from levy of GST on interest specifically excludes interest  charged on outstanding credit card balances as per serial no. 27 of the table of notification No. 12/2017-Central Tax (Rate) dated 28th June, 2017, as amended.

Q 46 of GST FAQs on Financial Services Sector published by CBIC