It's more than likely it's a scam call, I've had two or three of them and I'm not even a BT customer.
When you get the next call, and you will, just put the phone down and ignore it, eventually when they don't get you to bite they will stop or try something else.
Remember, these scam (scare tactics) calls are ultimately designed to separate you from your money.
My nan constantly gets these calls and did panic at first until I told her these scammers just use phone number generators on the off chance, the person on the end of the phone is with BT. How they can live with themselves is beyond me.
If you are ever concerned with your account, you can always call the official team. Just don't use the number from 1471. If you are a NOWTV broadband customer, the phone number will be under the Broadband & Calls section of your account, so they can put your mind at ease. 🙂
Yes, you are quite right, these scammers are usually calling from abroad, e.g. India, and are targeting the elderly and vulnerable, i.e. people that can easily be conned.
Unfortunately, along with the benefits of technology, such as extensive communications, comes a load of downsides, one of which is the proliferation of predators that think it is more profitable and easier to prey on vulnerable people rather than earn an honest living.
Because these scam calls come from abroad they cannot be blocked and are outside of UK jurisdiction. So please relay to your Nan that whenever she gets an unsolicited call, and she does not recognise the voice at the other end, then just put the phone down and do not worry about being impolite.
The best way to stay save from phone scammers is simply not to talk or listen to them, just put the phone down.