I tried rehab once and it didn’t work—why should I try it again?
If you have already been in rehab, it means you have already learned many of the skills needed to recover from addiction, and you should try it again. Relapsing (going back to using drugs after getting off them temporarily) does not mean the first treatment failed. People with all kinds of diseases relapse; people with other chronic diseases like high blood pressure, diabetes, and asthma relapse about as much as people who have addictions.
Treatment of all chronic diseases, including addiction, involves making tough changes in how you live and act, so setbacks are to be expected along the way. A return to drug use means treatment needs to be started again or adjusted, or that you might need a different treatment this time.