Wow, not only a problem with the machine, but a less than wonderful dealer to boot. I'd be pretty frustrated too!
There's a Yahoo group for Bernina owners that includes several models, one of which is the 830. If you go to Yahoo groups and search for Bernina 830, it should come up. There are some very helpful members and great suggestions there. Recently somebody with an 830 was having issues similar to yours. Another member explained how to clean out the insides of the bobbin area using a trident tool that Bernina supplied. It was amazing to see how much broken thread had worked its way in there!
I'd suggest joining the group and seeing if they can help you. And I'd be contacting Bernina about both the machine and the dealer. And I'll continue to be thankful for our wonderful dealer (Leroy @ Penn Yan Sewing).