I am having the same issue. My tiscali email has been hacked and my email address is being used to log into Amazon, eBay, PayPal, social media accounts, etc. I am unable to change the password for my tiscali email as I do not have a Talk Talk account, so cannot prevent this fraudulent use of my account.
Can you still sign in to your tiscali mailbox using the TalkTalk Mail sign in?
Have you set up password Reset details? Please do try the Reset your Password option. If there's an alternate email or mobile number shown that you definitely recognise from the hints, and have access to, then please reset the password.
If you can sign in to TalkTalk Mail then select the password reset to be sent to the account itself or, preferably, update Reset details via the main menu. Menu (triple line icon top right) > Update your reset details is in the sub menu.
If the self-help password change / recovery options aren't effective then let me know and I'll alert the TalkTalk Community team for you.
In the meantime, please update your Community Profile Personal Information (Click here) to include your name, current contact 'phone numbers and address with postcode (location) then scroll down and add the email address to Private notes and Save changes.