For what it's worth I got some compensation and a rapid exit (by MAC) after formally complaining about 3 months of truly awful service - followed Tiscali's process and escalated to the ISPA through all their levels (Tiscali just ignored it at first).
But I had to block the Direct Debit and be incredibly persistent and put everything in writing (which they never do). They have departments that just don't talk to each other and they were still chasing me for money (incorrectly) over 6 months after I'd moved on and the high-level complaints people had settled everything including the compensation!
I will never, ever, deal with them again and fairly obviously don't recommend them to anyone in any circumstances.