I suspect there's far more to the story than you suggest, and 20 years old is nothing, there's cable decades older

20 years old cable isn't a reason for Openreach to replace the cables.
FTTC isn't in trial phase now it's in commercial rollout, commercial as in looking to make money. Not a lot to be made spending loads of cash provisioning it to relatively few customers in small villages. It was trialled in a pretty small village and the odd one is being enabled but it's about where the money is and how much noise people can make about wanting the service.
Calling India - I presume this indicates you are a BT Total Broadband customer? If you aren't you're wasting your time and should be speaking with your ISP.
How do you know that it's the same fault affecting everyone? Do you know how far your line is from the exchange?
Are you sure there are issues logged at
your exchange every time you call? Which one is it? I can see all BT Wholesale fault reports for exchanges, just as everyone else in the country can.
Is
this a viable option?
Top marks for ranting on the post but absolutely zero detail for anyone to supply anything approaching good advice and a solution.