Depends on the agreement that you signed with regards to the refund. You could say you have changed your mind about the implant. Your medical records are yours, and you are entitled to pick them up from the office. Four days is plenty of cancellation time, but I would do it first thing on Monday morning and not wait. You will not get your money back right away, because bookkeeping will have to transfer funds. You should see it in two weeks or so.