A mega church involves a lot of politics and money. From what you've said, it sounds like they were all working towards a few of things:
Limiting your involvement, because they don't believe your skills are up to the task. They need to provide a high-quality product to a large congregation. That congregation has certain perceived expectations which have to be met.
By muting you, they limit the "damage" you can do to the product they're providing. They also allow you to participate in a harmless way. They're thinking they can satisfy your need to be involved and their need to have high-quality music, without hurting your feelings.
They're giving you some pretty strong hints that they don't want you involved, but you're not taking them. Making you audition four hours away, with one song? Muting you? None of that says, "we want more from you!" It says, "please go away."
You shouldn't be angry with the sound guy. It's very likely he's doing what he was told to do.