First, if it were me, I would follow the advice given in several different posts above and NOT send these borderline extortionists any money.    

Second, if you do owe someone money these people calling you are offering you no documentation that they are authorized to collect it -- it sounds like they are just fishing and trying to scam you out of money using general information they got from someplace and the probability is even if you owe money and make a payment(s) to them those payments will never be credited to paying down the actual debt.  The fact that they don't know how much you owe is indicative of that.

Third, even if you do owe a debt then that is a civil matter, not a criminal matter, and the police only detain and/or arrest people on the belief a criminal act has been committed (or due to a court issued arrest warrant) -- certainly not merely because someone tells the police you owe money.   To put your mind at ease about this, most police and sheriff's departments have a non-emergency information number.  I think you can call the police/sheriff, briefly explain the situation, and ask them if there is any chance you will be arrested on the say-so of these scumbags.    It also sounds to me that these callers are very close to making what is called in most jurisdictions something like "terroristic threats" as they are threatening what should be known to them is unlawful imprisonment and there is the vague "suffer consequences" threat as well. Terroristic Threats are a criminal matter.      

So, if it were me, I would just tell them that I will no longer discuss the matter with them in anyway, and they are not to contact me again, and if they want to pursue it further, then to file the proper civil litigation suit in the proper court in your jurisdiction and you will see them in court (which will likely never happen).    

Incidentally, it's not that I don't think people should pay their debts, it just seems that you are being scammed at best in this situation.