Harrased by the Nimble Group

Hi have been harassed by the Nimble group to pay an amount that I donot owe for Glo cell. When my contracted period came to an end. I called Glocell and confirmed that I will like to cancel. Although I canceled. I was continuously getting billed. Now that Glocell has liquidated.. The Nimble group has taken over the collection and I am being harassed daily to pay an amount that I donot owe. It's so frustrating. Each consultant that calls in.. I have to repeat the same story over and over.