Can I get my medicaid switched back to Straight medicaid from HMO medicaid?

I have pectus excavatum and I am with medicaid insurance. I was scheduled to get surgery June 15th and the medicaid was going to pay for the surgery but the surgeons office called me today and said that the medicaid got switched from straight medicaid to hmo medicaid and tha it wouldn't cover the surgery now. Is there any way to change it back and how would I do that?