Carol, I would just keep treating with the soapy water spray every few days, and also hose the plants off to wash off any aphids between soap treatments. My Blue Hawaii had a few aphids when it was very small, but soaping and washing cured the issue just fine. IF you persist you can win. A stronger chemical is not going to kill the aphids any faster or better. Dead is dead. Just be sure the soap gets down in the leaf axils etc.
Try mulching around the root zones of your plants with melaleuca mulch, too. It has aromatic oils that insects dislike, and I always find that after I put down fresh Florimulch, the insects are much fewer for weeks afterwards.
