You didn't "use" the new things but you get them now. They've spent 3 months developing stuff which you now want basically for free. Think about it as paying for work, it takes time to develop features, say 1 feature a week. You didn't pay for 3 months, they added 12 things. You now get them without paying if you were to get 12 months since renewal. It really is no wonder they don't want to offer that on a discount.