I've had this account 19 years, and not gonna lie this could be the one thing that would eventually make me quit. I don't play every week these days, so it's possible I've missed this so called "grace" period. Getting in touch with players support... how do you even do that, the website doesn't exactly make it easy? Hence posting here. Why not just make an easy update my payment details section?
https://support.runescape.com/hc/en-gb/articles/206377679-Recurring-subscription-rebill-failed - I would follow the contact us button at the bottom here which will give you an opportunity to speak to someone from player support.