I would type a letter up addressed to the manager of the practice and the doctor and send them both certified. Be sure to state in your letter that you are revoking your consent/signature and that at the time that you signed the "Refusal to Vaccinate Form" you were under extreme emotional duress (which means you were mentally coerced/bullied by the doctor). Be sure to state that you have since learned that you were lied to about vaccines/diseases. This letter hereby should find that previous form null and void. It also wouldn't hurt to state in your letter that you will be shopping for another practice who doesn't use such sly, manipulative tactics too!
For legal purposes, it wouldn't hurt to have it notarized too!
Please be sure to share your story on what happens!