I bought the 12 month subscription and then renewed my number and still paid 30/60 instead of what I thought should be 30/30 for this... Why?
Unfortunately I'm not entirely sure why you haven't received the discount.
I assume, because you purchased Online Number, right after you purchased your subscription. Perhaps your package has been activated with a small delay, so actually after you bought your number.
I suggest you to contact Customer Service and request a refund, and try again later on.
How to request a refund: https://support.skype.com/en/faq/FA297