[2020] Changing credit cards but I don't want to lose my $5/month rate

Hi r/runescape!

I've searched and searched for a way to do this properly without possibly jeopardizing my grandfathered rate of $5/month on my account, but I just can't seem to find a way and was hoping that someone might be able to point me in the right direction.

Things to note: I do not have access to the old credit card used for my membership subscription The 'update card' section leads me to the "packages" for subscriptions (monthly, Premier) but it is asking for the NEW rate.

I'd love it if a mod might be able to help, as I'm sure there are many other people who will run into similar situations, but if anyone has done this before, please let me know!