United Healthcare Misleading..replaced my Medicare wihtout my permission or knowledge Hot Springs Arkansas

I applied for supplemental insurance via the AARP website that hosted United Healthcare. 

I called my doctors office to schedule an appointment for a procedure and I was told that I would be required to pay total cost up front.  I asked why and was told that my Doctor did not participate in the Medicare plan I was on.  I told them it was the same plan I had been using for all the MRI's and consultations I had done the past few months.  They then informed me that I had apparently changed my Medicare.  

Well, you can imagine the surprise and anger I felt.  I am in so much pain and now this.

I had been speaking to UnitedHelathcare several times in the past couple of weeks because I had signed on with them , but only for supplemental.  They had been sending me letters regarding a prescription plan.  I made them aware I had a plan thru my VA benefits and did not need their plan and that this was only a supplemental plan.  I even spoke to them as early as that morning and was told by their reps that I only had a supplemental plan.  Not feeling good about this, I called Medicare.  Sure enough, United Healthcare had replaced my original Medicare plan.

Now I have to wait for at least 30 days before I can move forward with this procedure.  I am in so much pain..I have used up at least 60 minuets of my precious minuets on my cell phone plan.