You should:
A: Contact the seller, see if he'll refund you the cost of a replacement or repair.
C: Figure out how to fix it yourself. That's always a good thing.
B: Contact eBay if the seller is a jerk about it.
You can buy new foot controllers, both standard and electronic at Sew-Classics. You can also get one with a new wire and connector attached if you need to.
I don't know where to get genuine Singer controller, maybe I should look.
You've probably got a bad wire in either the cord block where it attaches to the machine, or in the foot controller. They really are not that hard to fix.
The one suggestion I have is this; if the wiring has the smooth outer shell with two strands inside, there's a very good chance it's the ancient aluminum wire with latex insulating. Replace it if it shows the slightest sign of deterioration.
Joe