OpenReach (the BT subsidiary operating the line network) has a clear (available on their website) policy for how their engineers should interact with people that includes guidelines for informing ISP-customers about who they are and who they represent (OpenReach and the end-user ISP) and how to deal with customers in a way that represents the ISPs well (the customer of OpenReach is the ISP - they're a service delivery company working on behalf of the ISP, not the end-user).
A few years ago some of this may have been confusing, as customers used to have to deal with BT directly, but now "everyone" knows about BT/OpenReach handling the installation on behalf of a lot (not all) ISPs, and every ISP I've had in the last decade has explained this to me when I signed up, and these days customers do not have to deal directly with BT other than OpenReach engineers. And people are used to outsourced service companies dealing with utilities. E.g. I get power from Npower, and over the years a dozen different companies have done meter readings on their behalf where I live.
As for your "Twinkle" and "Decker" examples, blame your ISPs that have decided to use this as an excuse for their own problems. In the Twinkle example, the ISP is a customer of OpenReach, not you, it is their responsibility to deal with OpenReach, not yours. If they're trying to push OpenReach in front of them, that's their bad customer service.
As for your "Decker" example, it's Decker's fault they've not checked coverage prior to making promises they can't keep. And "aren't allowed to run the fiber" == "we've decided (as most, but not all, UK ISPs) that OpenReach provides a good enough network for us, so we won't make any investment in rolling out our own, sorry". Nothing prevents UK ISPs from trying to build competing networks, other than the capital investments needed, and the low projected rate of return for most of them outside of the most densely populated city cores.
The relative lack of competition for OpenReach is a good demonstration that the market doesn't share your assessment of them. Many are unhappy with them, but not unhappy enough to pay for anything better.
OpenReach (the BT subsidiary operating the line network) has a clear (available on their website) policy for how their engineers should interact with people that includes guidelines for informing ISP-customers about who they are and who they represent (OpenReach and the end-user ISP) and how to deal with customers in a way that represents the ISPs well (the customer of OpenReach is the ISP - they're a service delivery company working on behalf of the ISP, not the end-user).
A few years ago some of this may have been confusing, as customers used to have to deal with BT directly, but now "everyone" knows about BT/OpenReach handling the installation on behalf of a lot (not all) ISPs, and every ISP I've had in the last decade has explained this to me when I signed up, and these days customers do not have to deal directly with BT other than OpenReach engineers. And people are used to outsourced service companies dealing with utilities. E.g. I get power from Npower, and over the years a dozen different companies have done meter readings on their behalf where I live.
As for your "Twinkle" and "Decker" examples, blame your ISPs that have decided to use this as an excuse for their own problems. In the Twinkle example, the ISP is a customer of OpenReach, not you, it is their responsibility to deal with OpenReach, not yours. If they're trying to push OpenReach in front of them, that's their bad customer service.
As for your "Decker" example, it's Decker's fault they've not checked coverage prior to making promises they can't keep. And "aren't allowed to run the fiber" == "we've decided (as most, but not all, UK ISPs) that OpenReach provides a good enough network for us, so we won't make any investment in rolling out our own, sorry". Nothing prevents UK ISPs from trying to build competing networks, other than the capital investments needed, and the low projected rate of return for most of them outside of the most densely populated city cores.
The relative lack of competition for OpenReach is a good demonstration that the market doesn't share your assessment of them. Many are unhappy with them, but not unhappy enough to pay for anything better.