My DD went through a phase like this as well, it wasn't too bad whilst she didn't have teeth, but it continued for a few days after those first two teeth arrived and it was a painful few days.
I did the "no" thing as well and finished the feed, but like you I don't know if she really understood. What I found is that DD would do it at the end of a feed if she wasn't really hungry and it was more playing, or if I was trying to feed her to sleep but she wasn't hungry. So she was happy to get down and play when I said "no" so it's wasn't that much of a disincentive iykwim.
What worked for us was, like tenar, to ensure that I only fed when she was truly hungry, and to keep a very close eye on her. I've read that it is physically impossible for the babies to bite when they are actively sucking, so I'd watch her closely when she stopped actively sucking, and if I saw her jaw tense, I'd remove her from the breast (using a finger to break the suction if needed). I'd offer again and if she was still hungry she'd keep eating, but if not the feed would be over.
I think I only needed to keep doing this for a week or so (the biting stopped after a few days, but I was a bit anxious for a while afterwards!).
Another thing to try might be offering a damp/cool washcloth or cool teething ring to bite on before a feed; or just after a feed when the active sucking has stopped, as that might help with the teething pain.
There was also a really good kellymom article I read on biting/teething when breastfeeding that helped me, but for some reason it's not loading for me at the moment (not sure if it's me or their website). But google gives this link which might work for you:http://kellymom.com/parenting/parenting-faq/teething/
All the best, hope this phase passes quickly for you!