Transaction problems

Every time I try make a purchase online, it goes through, but these days websites remember card details for easy checkouts. Let's say I want to register my card for PayPal, I cannot do this as PayPal requests to remember your card and deduct money to verify, and every time it wants to verify I get a nice message from FNB saying \FNB :-) Tranx declined due to CVV failure. 3 digit security number incorrect or missing in Tranx detail. Contact ***for assistance. 11 AUG 17:48"for example. It also happened the other day when I tried to purchase something"