I found an entry on reddit which was given by Jagex:
Original message details are unavailable. There was a mix-up in our email and the information on the billing page is correct. If you don't see the 75 extra keys offer, then purchasing the 75 keys package will just be 75 keys. If you've already purchased it, contact our customer support team and they'll help you out
Feel free to DM me your email address and I'll double check everything for you.
You can't really disable promotions. Checking the box saying don't display this message again applies only to the currently running promotion.
Jagex is using targeted advertising, and if you're already buying keys they don't need to entice you to buy more keys, so the best way to increase your chance of being targetted again for a future promotion is by not buying TH keys in the meantime.