This subject has been discussed in other posts here, you may want to use the search function and the term "usual and customary", and you will see what has previously been discussed. That said, here are a few things to consider:
2. Insurance policies have in network and out of network benefit levels. As an example, if I see an in network provider, I have a $250 deductible, and insurance pays 90% of U&C charges after that, and I pay 10%. If I see an out of network provider, I have a $250 deductible, and insurance pays 70% of the U&C charges after that, and I pay 30%. Either way, the charges are subjected to U&C rates.
For someone new to all of this, as you say you are, I can see where it doesn't make sense about the refund that was done. Hopefully, what I have said here will make it a little more understandable.