Resolved Question: Am I liable for my late father’s bill?

My dad passed in October of 2011, he did not have an estate because he was staying with me due to his illness. No executor has been named and nothings gone into to probate because he had no car or belongings other than his bedroom furniture and books. He did have life insurance of $10,000 which $8400 of that went to funeral cost. I just recently received a letter from a collector of his stating that he owes them $6000 and that I am responsible for the pay back, I am not even the eldest of my siblings. They state they are assuming I am the executor, I’m scared to call them because it’s not the actual bank that he owed money to, it’s a second hand collector that has bought his debt for pennies on the dollar. These are very crocked people and if I talk to them will they consider that communication to further pursue this debt making me responsible? I even think it’s out of it’s statues of limitations, my dad hasn’t had a credit card in over five years. What do I do about any other bills that are out there in his name. I don’t have money to hire a lawyer and am at a loss.