While I’m glad Graham Cannon found his solution to the hateful “sales” calls, the real culprits are BT themselves!
While they are content to milk the bill-paying customer with ever-increasing line rental and call costs, they make these nuisance calls possible.
How? By selling huge bundles of calls at ridiculously cheap prices to the sharks that make them. If they stopped doing this, then these calls would be unprofitable and so stop.
BT aren’t alone. Most mobile companies do the same, hence PPI and “whiplash” texts that plague your mobile.
It’s like someone punching you in the face, then selling you an aspirin ...