Actually, you CAN NOT GUARANTEE any debt is valid. JL Teamworks is taking the information they get at face value and do not know the validity of any bill. I have received calls from them trying to collect a debt that I do not owe. After some time and considerable headache on my part they finally stopped calling.
My advise is to send them a certified return receipt letter demanding proof you owe the bill within 30 days. Include in the note that just saying so does not make it so and that you want to see copies of the original bills. If they fail to provide you with such proof then tell them to cease and desist all collections and file a complaint with the FTC (they have a handy form on their website). Failing that, take their incompetent behinds to court.
Should they provide proof and it's legit, then pay up or make arrangements. It's their responsibility to prove to you that you owe any debt and should not be harassing anyone. Likewise, if it's your debt, it's your debt.
Just got a call from JL Teamworks - when I answered they started trying to get personal information about my husband. I kept asking "why" and they said that they could only tell me if I gave the last 4 digits of my husband's social. I said goodbye and hung up. VERY SUSPICIOUS!