If you get unsolicited calls from numbers you don't recognise, then make a note of the number and go to www.phonespamfilter.co.uk
then enter the phone number in the search box. It is possible that someone has experienced this caller before and has entered the details of who it is and what they tend to want (e.g. your mobile phone company on autodial trying to flog you stuff).
What I then do is add the phone number into my contacts with an appropriate name so that if it calls again I quickly know whether or not to ignore it.