Thats what mine was like with Tiscali at my old lasses house. Kept getting cut off, and off for a day, 2 days etc. Phoned them up and played hell with them, of course, it wasnt a uk call centre either, so i kept asking to speak to someone english, or someone i could understand anyways, eventually, they sent me out a new modem, and have not had any problems with it since.
Just a thought, but maybe say your model is faulty, and ask for a new one. Might solve the problem, might not. They could just say they are servicing the line, so they dont have to look into any problem etc.