<prompt> Human: I had a surgery last month; I verified with hospital several times before about the expenses. They assured me that they accept my insurance, and I have only to pay the deductible amount. Today, I got a bill of 4200 from the insurance company saying that your hospital has used out of network service provider. Please help.  <response>: I got a bill of 4200 from the insurance companyInsurance companies dont send bills. They send you an Explanation of Benfits EOB that describes how they handled your claim.Also, just because you have insurance doesnt mean everything gets paid. If youre in a high-deductible plan you could be responsible for the first several thousand dollars of your medical care before your insurance company starts paying.And just because they denied it doesnt mean you are responsible. If the hospital is in-network and used an out-of-network provider, the insurance company might require the hospital to eat it.So we need to get all this straight before we can give you advice. Did they deny the claim, or apply it to a deductible, or deny part of the charge as being over their contracted rate, or what? the insurance company saying that your hospital has used out of network service providerIf you really are being told you are responsible because an out-of-network provider was used, insurance companies typically decide how to handle this by looking at who was directing your care. You likely did not just decide to go to a hospital. You were seeing a doctor who told you surgery was required. So, who was that doctor? Was he in-network? If so, you can make the argument that you were following the directions of an in-network doctor so should be held harmless.Also, the claim could simply have been processed wrong. I worked in a claims department a couple of decades ago. It was complicated and many mistakes were made. I verified with hospital several times before about the expenses. They assured me that they accept my insuranceIn the future, you need to also verify with your insurance company that the providers you are using are in their network.tl;dr Your post contains some misinformation. We need to know exactly what the insurance company told you on your EOB. It would also be useful to know what doctor referred you to the hospital and what that doctors relationship with the insurance company is. 