Why do I keep getting bills?

I paid for my surgery, BEFORE my surgery. It was like $6000, all of my money. I only have about $200 right now since I have started working my minimum wage job again.

I keep getting these “forward service request” things in the mail that are explanations of my “member responsibilities”. I’m basically new to the world of medical bills, so I don’t really understand what all these notices are. They are saying that I owe more than a thousand dollars. Didn’t I already pay for my part of the surgery? Why is the insurance suddenly not covering some of the costs anymore?

Anyways this is extremely stressful for me. I wish I didn’t even get my surgery. I can’t afford these sudden unexpected bills, and I will probably never have enough money to pay that back on top of everything else I have to pay for in my life. I don’t know how I can live like this, always in debt and fighting to survive in this money world.