Are These Colonoscopy Charges Normal?

Hello all,
Not too long ago I went and had a colonoscopy and endoscopy procedure done at a surgery center, despite being told by my doctor it was in network… it wasn’t, the surgery center claimed they called me and talked to me personally about the cost of their out of network facility… they didn’t… anyway…
They charged me 36,000 dollars for the two procedures, took off 21,000 in “contractual write offs”, and my insurance paid them 13,000. Long story short, is out of network colonoscopy/endoscopy usually so much money with those write offs? If it isn’t, is there ANY oversight/government oversight to health practices charging so much for simple procedures?
I am also located in California.
Thanks!