An active, advanced infestation of scale insects is difficult to control with most insecticide contact sprays, horticultural oil or organic botanical repellents because the adult scales are protected with a waxy covering.
For fast and inexpensive control, I would use Orthene or the generic Acephate97Up, mixed in an ironing type spray bottle and applied directly to the foliage where the scale insects are implanted and feeding. The material is systemic and readily absorbed into the leaf surface. Its a stinky, older generation organo-phosphate insecticide, but it works, and fast. Follow product label directions for safe and effective use. It is low toxicity for mammals, people and pets, but toxic for fish and bees.
There is an alternative that can be applied to the soil for root uptake, so you don't have to spray. Safari is also a highly mobile systemic insecticide and it is not stinky. But it is considerably more expensive.
After this current advanced infestation is controlled, you can take up a preventive program with twice a month spraying with neem oil or another organic/botanical type of product: