Sorry to hear that but once they have made 'first contact' with you, more calls will often follow.
If the calls become too much, you could look at a call blocker device which screens out the calls and prevents them ringing through to your phone.
I recently posted some extended info. on using a trueCall device here
https://community.virginmedia.com/t5/Home-Phone/How-do-I-change-my-Virgin-Media-landline-phone-numbe...
and here
https://community.virginmedia.com/t5/Home-Phone/Nuisance-Calls/m-p/4324071#M136451
This has totally solved the problem for me and screened out all the unwanted calls. You could also look at
https://www.cprcallblocker.com/
which has a range of devices at cheaper price points but perhaps with not so many fine-tuning features of the trueCall device.
BT also offer a range of call blocker phones. The simplest ones offering blocking of individual numbers are not much use since the caller ID numbers are invariably spoofed and change for each and every call. Some of the BT phones offer trueCall features but there have been a few mentions on these forums about issues with them not working reliably with VM caller ID (though it is not clear if this is a VM caller ID problem or a BT phone problem).
If you look at buying a blocker device, check out the online reviews of the device before purchasing for any mentions of problems on a VM landline. Also make sure the place you buy it from has a good returns policy in case you run into any technical issues with it.