Some (unsolicited) advice:
You say you can't face the hassle of changing e-mail addresses, notepaper, etc as a result of migrating to another ISP.
Well, consider this; I've now been in dispute with Tiscali for 16 months, in which time they have displayed constant technological ineptitude, administrative inefficiency and a total lack of customer care.
Back in 2001 Tiscali bought out the old LineOne ISP with which I had my primary e-mail accounts. In December 2001 they attempted to merge/migrate the LineOne dialup databases with their own - and totally 'screwed the pooch' as our American cousins would say. Result: I was unable to access the internet at all for a period of about three weeks - no warning, no advice, nothing. Unsurprisingly, I decided to cut my losses, cancel the LineOne (Tiscali) account and join another ISP.
Happy ending? No, Tiscali continued to charge my credit card £14.99 per month for the pleasure of not accessing the internet. I shared your experience of spending a fortune in both time and money trying to contact Tiscali customer service by telephone (and e-mail) and eventually thought I'd cracked it in March 2002 with a registered letter formally instructing them to cancel my account and to cease and desist from billing me for a service I wasn't receiving.
Bingo! (I thought) June 2002 sees another charge to my credit card - a small one which I eventually ascertained was an 'account finalisation'. OK, the initial breakdown in service didn't happen on the last day of month, so perhaps that was fair, but Tiscali didn't see fit to send me a closure of account statement.
September 2003 showed why. Tiscali again charged my credit card £14.99. Several (expensive) calls to Tiscali customer support only highlighted just how confused, ineffectual and inefficient is their billing, account management and customer care organisation, and necessitated another letter, this time with proof of the charge to my credit card (because 'it didn't show on their billing records'), again demanding a cessation of billing, cancellation of any direct debit and reimbursement of the £14.99.
I have received no reply. OK, Tiscali haven't billed me again (yet) but I again called customer support in November 2002 to be told that their billing department 'had a backlog but that my claim would be processed within 30 days'. Over 120 days later ...... no reimbursement and absolutely nil communication in any form from Tiscali.
A third 'stroppogram' letter has just been dispatched to Tiscali, but I won't be holding my breath for any reply!
My advice Goldcroft: unless you have a substantial sum tied up in headed notepaper, type that simple e-mail to all your contacts announcing a change of e-mail address as from a given date (stating the reason why) and make that migration to another ISP. It will be less painful in the long run.