Accidentally extended extra boost for a year

I won a free month of nitro classic, but didn't care for it. I bought a month of nitro, and decided I liked it better, so after a few weeks I decided to switch to the yearly plan. While I had classic, I bought a server boost. When I switched to regular nitro I canceled it, because I didn't want to continue paying for a third boost. When I went to switch to the yearly plan, it told me I had to uncancel my boost first. "That's weird," I thought, but I did it. I switched to the yearly plan, payment information was already saved, clicked through... then realized the price had been higher than I expected. Sure enough, it renewed the extra boost I didn't want for an entire year, without ever actually mentioning that fact outside of the price being higher. Should I have double checked the price first? Of course. But why in the world can't I cancel one thing and renew another? If I click that I want to switch my monthly nitro to a yearly nitro, nowhere in that did I ask for any other subscriptions to be changed and they shouldn't be.