Whether you keep trying or not is definitely your call. It's neither right nor wrong to withhold that information, simply a choice. Many people decide to keep their religion secret, and find it to be more meaningful to them that way. Others are very close to their families, and therefore feel obligated to clue them in.
It's unfortunate that they have felt the need to force their beliefs upon you like that, but I suppose this does happen to a lot of families. I was brought up in a Protestant household, and my mother was my Sunday school teacher. Luckily when the time came where I got up the nerve to come out of the proverbial "broom closet", she was surprisingly understanding and supportive. The only person in my immediate family at this point that I don't think knows is my dad. I feel like if I laid out for him EXACTLY what it means to practice witchcraft and successfully nullify all of the horrible stereotypes, he would be okay with it. Just last night there was a less then tasteful depiction of "witches" on the news, doing a banishing spell for Charlie Sheen's negative energy (sheesh), and my dad responded with "Well it looks like we're not dunking witches anymore?" (or something along those lines). Took everything I had not to turn red in the face. A lot of this stuff is pure ignorance, and I suppose the stronger your belief system is, the harder it is for you to accept ANY religion...even aside from witchcraft.
Getting back to your problem (sorry for the brief divergence..), if you really want to tell them about your chosen path (which is perfectly noble and understandable), perhaps you should try to explain to them how it hurts you that they're not willing to give you the proper time to explain yourself, and the only reason you wish to explain it to them is because you care about them and want to clue them in to your life instead of shutting them out (which many teenagers do). Also try to get them to understand that you're not trying to rebel against them by choosing witchcraft; that it is a serious life choice, and since you have given them respect in their religious beliefs, that you'd appreciate it if they could stop and listen to yours for a moment. Trying to reach a base of mutual understanding is key, and going about it in a fashion where both you and your parents can speak on the same level. Try to sympathize with them. Yes, they are being a little callous, but it's something they're not used to. In a situation like this, patience is definitely beneficial.
And if worse comes to worse, if they don't listen, you have a community of witches who have your back and can sympathize with that emotion. Even in the past 50 years, much of the stigma that was once associated with witchcraft has begun to dissipate, and this is in direct conjunction with witchcraft/wicca becoming more mainstream. If your parents don't understand your path now, hopefully someday they will see the error of their close-mindedness.
Bright Blessings and best of luck. Feel free to PM me with any concerns or if you just want to talk.
"Oh, do not tell the priest our plight, or he would call it a sin,
But we've been out in the woods all night, a-conjuring summer in,
And we bring you good news by word of mouth, good news for cattle and corn:
Now is the sun come up from the south, by Oak, and Ash, and Thorn."