Was out of network since January and received a $700 bill

I got diagnosed with sleep apnea last year and my ENT started me on a CPAP machine. I was only willing to do so if it was affordable and I stated that many times. So I got the machine in December 2023 and I was told after paying the $350 deductible I would be charged $36.94 to rent out the machine monthly. I was also told that the machine would mine after six months of use of consistent use. Well I was checking my mail yesterday and got a letter from the supplier saying on June 17th I will be charged $638. This is the first bill I received from the supplier company and it is for Jan-May. I talked to my insurance and they informed me that they have not been in network.

I went to my ENT appointment and they or nor anyone else informed me that there was no insurance coverage. I made sure to ask the person who supplied me with the machine if I would be covered for 2024 and everything that needed to be asked in terms of insurance. I knew that there was a chance for my insurance to change when the 2024 plan started and I was assured that I would still be in network and had nothing to worry about. It switched as I had thought and the medical equipment company never said anything.

I am wondering if there is anything I can do? Or anyone else? I have reached out to my insurance, the medical supply company and my ENT billing department. I was told that I would not be surprised with this bill when I started using the CPAP. I said so many times that if it is not a finical strain I would do the treatment. I asked all the right questions and made sure, but at the end was still left in the wind.