I don't know how we are going to pay our Dr. bills

Just over the past 2-3 months, I have accumulated about $1,400 in Dr bills (after insurance) and I know my husband has some overdue bills from a couple years ago. They sent me a letter yesterday saying I have to pay around $300-400 within the next 3 weeks. There is no way I will be able to do that. What will happen when I don't pay in time?

I know I will have more appointments coming up in a few months and it makes me scared to even go to the Dr right now.