10MB line, up to useless!

We have a 10 meg line with Openweb, and it works great! Between 8pm and 6am when nobody needs it..... The rest of the time it takes 20 minutes to load a simple page, IF it even bothers to load at all. And I'm not even going to mention download time. I don't download a load of stuff, and I don't consider myself an overly active internet user. Having a 10 meg line, I expect it to at least work half decent during business hours. Not the first time either! Useless useless useless internet provider. And so unwilling to do something about it.