Debt collection agencies often will harrass you, calling at all hours and threatening to take you to court, but they won't. Be carefull if you do call them because if they get your number you will get calls at all hours of the day, several times a day. I don't know where you are, but in Canada, if you request that they only contact you in writing, by law they have to abide by that. You do have rights!
Write to them and tell them you have no idea what this is for and that you need proof and statements showing why you owe the money and how they arrived at that amount. I wouldn't just pay it without any documentation. If they can't come up with something with your signature on it, then how do you really know it's your debt? These companies do make mistakes. I have two different bills coming to my home on a regular basis and they are definitely not mine. The last name is correct, but the first is not and no one else has ever lived at this address!
If they can come up with proof and you do agree that you owe them money then you do have to pay...your marital status at the time and the fact that you are now divorced doesn't matter. Unfortunately, if the debt is only in your name, then I believe it will be your responsibility alone.
Recently, there was a spot on our local news about collection agencies, their harrassing tactics, and individuals rights.