It's nothing to do with already having fibre.
The Talktalk website just point blank refuses to allow ADSL orders if fibre is available and the ADSL estimates are very low.
It doesn't matter if I try transfer my existing number, get a new number or get a whole new line installed. The Talktalk site just refuses any ADSL order from ANY address on my street.
Cashback offers tend to be better for taking fibre.
Why not check what cashback is available for fibre and see if the extra cashback outweighs the extra monthly charge for it?
Thanks for confirming that you are finding the same with the TalkTalk website. I was beginning to think it was unique to me, despite trying their site on different browsers and devices, going Incognito, using a VPN, not using a VPN, etc.
Thanks for the suggestion re cashback. I can see a spreadsheet looming. However as I mentioned earlier, it is frustrating having to enter my details, only for many of them to say they are not actually available, or at least the offer isn't. Plusnet was one example. Not Available via a link/offer on MSE, yet going direct without the offer it was available.