I also have receive calls from what sounds like an indian bloke to say theres some thing wrong with my computer, and I have also tried all the tricks but they still ring back.
It got that bad one day with more than 10 calls so I ask for there number to call them back and they gave me it. When I ring it they did answer and yet still saying my computer will shut down.
I now found this site to report things like this
www.actionfraud.org.uk give it ago see if they can help