Hello experts!
Here is briefly what happened. My wife had dental surgery in June. We paid a small portion (~$50) of the total ($900) at the desk and the rest was supposed to be covered by insurance. A couple weeks later I've got the bill from the doctor for the rest of the amount ($850) and paid this by cash too, assuming that the insurance payment will come later and they will reimburse me (this already happened a couple years ago). Then, I've got explanation of benefits from my insurance stating that it paid the doctor about$350 and the rest $500 is write off (goes under provider discount/disallow title). I called the doctor's office approximately 3 weeks after and they told me that they did not receive anything from insurance, although they are not 100% sure because the checks sometimes (by mistake) could be cashed without a record. I called the insurance and they told me that the check was sent to the doctor's office about 3 weeks ago. They refused to tell me whether the check was cashed or not saying the provider should call them for such an inquire. Then I called back to the doctor and the receptionist said she will call the insurance but not immediately since she is quite busy working at the desk. Now, two weeks passed since that day and I did not hear anything from the doctor's office. Here is my questions: - how much they should reimburse me (provided that they've got this payment from the insurance),$350 or \$850?
- how long they are allowed to delay this?
- I'm going to call the dental office once more, but if they don't seem very cooperative, what should be my further steps?

Thanks!