Just set this up for my mum and you can use it on BT Basic! She was getting calls claiming to be from BT. But my mum will play the game! They clearly are not from BT. Had to set this up manually could not add it online.

Got to be worth a punt as it is for free! And good if you use BT Basic

So added thus free service and
BT Call Protect - 'How to...' guide
BT Call Protect helps to prevent unwanted nuisance calls. By managing your settings, you can decide which calls you want to send to a junk voicemail.
Customers with this service can send calls to their junk voicemail by setting the preferences below:
BT Blacklist - We've identified a list of nuisance callers. Calls from these numbers will be sent to your junk voicemail. Our blacklist will significantly cut the amount of unwanted calls you get. We’ll turn it on by default when you get BT Call Protect
Personal Blacklist - You can add the last call you answered from your home phone, or any other phone number at http://www.bt.com/mybt - Inclusive extras to your own blacklist. This means that any future calls from those numbers also go to your junk voicemail. This feature will also be automatically switched on, but won’t have any numbers until you add some
Individual Call Types - You can choose to send all calls from certain categories to your junk voicemail. The three call types are:

✓ International numbers
✓ Withheld numbers
✓ Unrecognised numbers (shown as 'unavailable' on caller display or on 1471)
If you don't already have BT Call Protect you can order it online at: http://www.bt.com/callprotect
Once you've got it, you can manage all your settings online via http://www.bt.com/mybt> or from your home phone by dialling 1572, which is free.
Click on the links below to find any help you need:
Getting started
Accessing the portal (My BT & BT App)