I managed to chat to someone at F-Secure about this issue and this is the result:
Seth (19/03/2018, 11:48:32): Hi David
Seth (19/03/2018, 11:48:35): We are from the F-Secure Consumer Support Team, focusing on F-Secure Antivirus and F-Secure Internet Security from our F-Secure website. The software you are using from your Internet Service Provider is a customized version of the F-Secure security program. F-Secure has only provided your Internet Service Provider its technology to customize the program for their customers. As such, your Internet Service Provider has a dedicated Technical Support team who would be able to support you. We recommend that you contact them directly to obtain further support. If they are unable to resolve the issue, please get your Internet Service Provider to escalate your case.
Seth (19/03/2018, 11:49:28): Thank you for using F-Secure Live Chat. Bye.
So... the ball is back in TalkTalk's court, but who do we contact at TT. When I chatted to a TT 'technical ' adviser I was told to contact F-Secure. Have they read Kafka?