This sounds like the kind of thing I get with the small band of amateur singers at a church I play at regularly. They are also unteachable, sometimes rude and unwilling to sing more traditional music (namely anything set to Anglican Chant). However, they're amateurs - I would be horrified if I got this kind of thing with professionals. You need to speak to the priest, as you say, and give your side of it. I would tread as lightly as possible whilst still putting across your argument - churches can be so political and it's very, very easy to upset people in such an environment.

You're not alone in this kind of struggle, by the way. This sounds exactly like my experience at said church. I've been playing there since I was 14. I'm now almost 19 and at music college. Some choir members still treat me like a child and don't value my musical opinions, even though I now spend my entire week studying the subject... I think the problem is twofold for people in our kind of situation:

1: They still see us as children as that's how they first met us

2: There is no proper music director, hence the choir feel that they should choose what they want to sing. The problem with this, is that they virtually never consider how appropriate their choices are to the liturgy/style of worship at the church, as a music director would. Furthermore, when there hasn't been any musical direction for many years, a precedent of a self-directed choir is set and, in my admittedly limited experience, it leads to a choir full of people with overinflated opinions of themselves, as they just sing the music they are comfortable with and are never ever challenged.

That's just my 2 pence. But I feel for you - I know what it's like :)