Am I supposed to be charged for postponing my surgery due to a positive COVID test result?

I've just had two separate reconstructive surgeries for eyelid retraction. My 1st surgery was originally scheduled for May 26 but I tested positive and the surgery was postponed until the following week. Right after the first surgery, I was told to be charged a fee of $7,500. And then, after the 2nd surgery, I was told that the fee was reduced to $750 after I complained. Is it a normal practice for doctors to charge such a fee even though postponing was out of patient's control?