Tiscali... ouch!! Heaps of people have had trouble with them - either throttling downloads or blocking ports (I know Tiscali say that they don't do this but there's a lot of evidence to suggest that they do!!). There are a couple of links below, if you search on Google then you're bound to find more.
SICK of TISCALI 's bulling tactics - ISPreview.co.uk Forum
View: ISPs the cause of COD4 problems?

Use the forum search to look for Tiscali. You'll find lots of past threads. Changing ports has helped some people, but hasn't worked for others. Did you try changing ports?

Yep, it seems like people in some areas have huge problems while people living in other areas don't. I can't explain that one Honestly, I don't think that calling Tiscali will give you any joy. They're either going to deny everything or may say that you've been a heavy bandwidth user & so have had the Fair Usage Policy applied (where they limit your download speed).
Tiscali - Fair usage policy

If you want to use p2p programs without these limitations, my best advice would be to change ISP. If you're stuck with Tiscali then at least try changing ports - it might help