Original message details are unavailable. Yes I've seen that. RS3 is extremely confusing to me as i don't play it. where is this "contact us" button at?
If you scroll to the bottom of the page, under "If you have completed the steps above get in touch with us through the contact option below so we can resolve your issue," there is a big yellow button that says 'Contact Us'. Right at the bottom of the page.
As this thread pertains to a billing support issue, I'm going to slide this thread over to the Payment Support forum. The advice left above by 0815 and Chief Elf should help you resolve this issue, but if you have any other follow up questions, don't hesitate to ask.