Hello Jane, I'm so sorry to hear of this. Typically a green shade occurs after first use, while the dye oxidises on your hair, and dissipates after 48 hours.
We would always say to do a strand test before first use to avoid any unwanted outcomes.
As the Auburn is quite high in Henna it's unusual to hear of someone getting a black shade on their hair; and usually with lighter hair it will come up lighter than anticipated. Sometimes previous dyes, or products, can affect the outcome of the Henna; if you'd lightened your hair at all previously this may have affected the outcome.
Please do get in touch with us via customer service with your order reference so we can try and assist you further.
With Kindest Regards
Rebecca