How do I cancel crossover benefits with medicare after retiree benefits canceled

On Jan. 1st of this year Country Financial canceled retiree benefits and we had to get our own insurance coverage.  Now Medicare says I have to cancel coordination of benefits with BCBS of Illinois as that is where they have been sending stuff too although they also have our new coverage listed .   Please advise how to cancel this with BCBS of Illinois so my doctor's office is not getting stuff from BCBS instead of Florida Blue.  All my doctor's have the changed insurance information.  HELP!