What is the period relating to the Law of Prescription? Is it three years?

I have just had a call from some law firm, demanding that I settle an outstanding amount owing on a Woolworths Visa Card that I closed more than three years ago. Since then I have never been sent any written demands/statements, nor have I admitted any liability on my part.

I feel that this law firm is taking a chance and they are hoping that I will acknowledge the debt.