I had a hair transplant one year ago and nothing grew out, what should I do?

A failure of a hair transplant is most often a reflection of the techniques used. If I had a failure, I would perform the next surgery at no charge. Yes, by all means, go back to your doctor and ask about why it failed. Assuming that you do not have some dermatologic disease that caused the failure, your doctor should make things right with you financially.  Ask how he/she will make sure it does not happen again. Ask yourself if you trust that the doctor will get it right the second time.