This is the problem with using 3rd parties to supply broadband. I had the exact problem as no fooker wanted to deal with the problem.
However they dont like it when you ring the every hour for an update. At least with pipex you get to speak to some one who speaks our language. Onetel call centres (who im with) are pants.
I think you have a fault on the line. They had to change pairs in the street as there was an earth problem.