Is it safe to provide 16 digit card number to the customer support Agent in the billing account security department

If you're buying something or have to pay for something you're going to have to.

Did you call them or did "Apple" call you? Notice the quotes. Apple won't call you unless you specifically ask them to. There's plenty of scams from fake representatives of real companies.

If you asked them to call about use of your credit card then they might need to know the number in order to see if it was also attached to any accounts other than yours. Anyway, if you asked them to call you then I would suspect all is above board.