How to convince my parents to let me have contact lenses?

I am 15 now and I want to have contact lenses. I want them since I turned 12. I tried to convince my parents to let me have contact lenses for several times but until now, all of them failed. I searched information about contact lenses wearing in the years so I know some information about contact lenses. My room is tidy (tidier than my parents' room). I always hand in homework on time. I study for tests and exams without the need of my parents reminding me. Cost is not a problem as my parents spend quite a lot on me (some of the costs are unnecessary that I can let them cut that off). My father stopped wearing contact lenses 12 years ago and is wearing glasses now. My mother do not need any vision correction. They said that I am too young for contact lenses that my eyes cannot be adapted to them (which is not true, the eyes of children can also adapt to wearing contact lenses). They also said that contact lenses causes the cornea to have not enough oxygen (there are contact lenses with high oxygen permeability). When I tried to explain to them about the facts and my points (in a polite and mature way, allowing them to think about it), they said no and change the conversation to other topics immediately. When I tried to change back the topic, they change the topic to other topics immediately, or told me to stop mentioning contact lenses. This happens every time. How should I convince them to let me have contact lenses?