Well check this! When I joined TalkTalk it was with a BT number, no problems until I called customer services for something. After each time I called I used to be plagued with these calls.
I moved and TalkTalk gave me a new phone number, a number allocated by them. I was plagued even more with scam calls.
I switched to BT and for some reason they ported over my number which I didn't want anymore, strangely as soon as I switched to BT, the scam calls stopped.
I reported this issue to Dido Harding, I received no response from anyone at TalkTalk.
This goes to show what a bad company TalkTalk really is and they have no right to challenge BT on Openreach, TalkTalk invest very little on infrastructure and by the looks of it they spend very little on customer services.