Ambulance Charges

So back in 2015 while in college (still in college) I had an incident where I was kinda forced to get an ambulance ride to the hospital. Well I had to accept and long story short I got charged $900 for the ambulance ride. The charge was for "Emergency student services". I blew them off and now I got called again to pay. Apparently I owe the money to the city itself not the ambulance company. The call came from a collections company and they said they cant force me to pay, but they just wanted to know. I told them to lower the cost and we could start negotiating. He said he would send me an email with a response which I never got. I just wanted to know, if I never pay this off or I tell them I don't have any intention of paying what problems can this cause for me. A friend said that student loans and medical bills never affect your credit score so Im glad its not affecting that. Is there anything they could do to harm me? I mean they can't really do any physical damage, but mess with my credit, put out a warrant something like that? Thanks in advance.