After you file

DO I need to report my 1095-C that I had health insurance? Just now got it in the mail after already filing. I was to get a refund of  $533.00. Did not get because of a mistake. I Also got a CP11 That I owe $867.00 to IRS. Not sure why. I tried many times to call IRS, but always says they are overloaded with calls and I can never get through to them. Please help, What should I do?

Thak you, Jason L Rudy