BCBS Coverage for Diagnostic Mammogram/Ultrasound

I had my annual physical done in September and was told that a lump was felt on my left breast.  I already had my yearly mammogram scheduled but the doctor indicated I needed a Diagnostic Mammogram and Ultrasound instead.  The appointment was yesterday, 10.10.22 but when I got there I was asked to pay upfront because our insurance does not cover the cost of the two tests.  Please help me understand why?  I did not get the tests done because I didn't have the money, which would have been over a thousand dollars, or if I paid up front $701.00.  I guess what I need to know is what does BCBS cover and how can I go about getting these tests run?