What good is Medicare if your doctor won't take it?

I would like to be able to opt out of medicare and have private insurance only.  I had no choice but to pay into the Medicare system through taxes that were required to be paid by law. I would like my money back in the form of a tax credit that I could use toward the payment of a private insurance policy . I already pay a substantial insurance premium for a medicare "supplemental" Blue Cross Policy and would be willing and,  more importanly , able, to pay more if I could get a credit from Medicare. Is this possible or , by going private, do I loose all the money  and benefits I already paid for?