Northern Leasing Systems Inc Northern Leasing Thieves New York, New York

I just received a bill in the amount of $1,500.00 for a credit card machine, for a company I don't own and never have owned. My father passed away from brain cancer over 3yrs ago. He was the owner of a small business. I contacted them today and asked them what this was about. They said I was the personal guarantor for this account and I have to pay the bill that is due. If I have no ownership in the company once so ever, how can I personal guarantee for a service without consent from the owner? She said that doesn't matter and I was an idiot for signing something that I knew nothing about. Then they tell me they will sue me if I don't pay? My question to them is, if the services started after my father was admitted into I.C.U. How can my father have an account for his business with them? Wouldn't they be missing some important signatures, like the owners? This is a terrible company and a horrible way to do business. Thieves~