Dental Works

My primary care dentist took an xray and referred me to get my wisdom teeth out because it was already coming out and giving me much pain. Went to dental works and set up an appointment and everything to get it removed. On the day of, they made me sign some receipt and made me pay my portion of the insurance/deductible before the surgery. Charged it to my card and weeks later I get another bill saying I owe another $1000 because somehow in the midst of couple weeks after the surgery, it got billed to medical, not my dental plan. I tried calling the office many times where I was put on hold for more than 20 mins each time. The receptionist admitted they see our caller id so obviously they were being very unprofessional and avoiding my calls. They somehow billed my insurance to medical by using a medical diagnosis code and not a dental diagnosis code and they are trying to overcharge my insurance and myself with my deductible being different with medical. I asked them to call me back but nothing and when I call, can never get a hold of them. Can someone please help with this matter. I can't get into touch with anybody in that office with me because they screen their calls. I called with a different phone and they answered within 10 seconds yet told me nobody was in the office. I have proof of xrays from my other dentist and have referrals and is ready to open up a case with the insurance with this scam they are trying to pull. Please can someone help with this? I just don't understand because when they gave us an estimate the total was $1800...in which I paid $800. Now they are claiming $4000 to my medical insurance in which I owe $1000 more (remember I already paid $800 upfront)... How? Did they do something different while I was sedated? How did a $1800 surgery change suddenly after the surgery to $4000