The aims of these scam calls are various but may include: identity theft, gaining access to your computer to steal personal information, gain access to your online banking to steal money, getting you to connect to a premium rate phone number by pressing a button to continue the call etc. etc. etc.
You may find this government link useful for advice
Unfortunately, if you have received one call, you may well receive more. If you received the call on your VM landline you could consider using some sort of call blocking/screening device or similar phone which can usually filter them out if the number of such calls becomes too great.
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.