I usually pay for my membership with my dads credit card (I pay him for it every month in cash), however it seems jagex is having a problem with paying with it at the moment. I type in the full details, including full name, address etc. But when I click accept it says that the payment is declined due to either fund problems (not this because my dads credit card has enough funds, he checked), or the details are incorrect (not this either, because I double checked the details, which are the details I always use to pay for membership and have used in the past). Could anyone give me a clue to whats going on here?

my memship ran out on my pure and im still paying but he's still f2p, of course theres no way of contacting jagex so i suppose just wait it out..

Try submitting a billing query, just use the search feature.