It's hard to diagnose the shrub with this much leaf damage. Did the foliage look this bad before it was sprayed with Sevin? If not, the Sevin might have caused phytotoxicity, which is plant tissue damage from chemical exposure. The active ingredient in that pesticide used to be carbaryl, but is currently probably a pyrethroid like zeta-cypermethrin. Both are broad-spectrum insecticides that have an equal risk of harming beneficial insects and pollinators as it does treating a pest. The pest insect should also be positively identified before using an insecticide, since the choice of chemical for control (if one is needed) will depend on what kind of pest it is. The most common insect pest of roses is a caterpillar-like larva called Roseslug Sawfly. Management tips for that insect can be found on the linked page. We see some sawfly damage on the plant pictured, but not much. Since you already applied at least two Sevin doses, any sawfly present might already have been killed off for now.

Roses are vulnerable to a range of pests and diseases, including more than one type of virus. We can't rule that out from the photos, because the symptoms are not distinct enough and are hard to distinguish from whatever overlapping issues might be present. If a virus is at least partially responsible for the leaf damage, it will not be treatable/curable. Leaf fungal infections, in comparison, tend to be more minor and treatable (by way of preventing new infections) with a fungicide. For now, since we can't identify the exact cause of damage and because it might have greatly weakened the plant already, you may want to consider just replacing it. Some rose varieties are more disease-resistant than others. Knock Out series roses do have some above-average disease resistance, but still can contract a few infections, including one or more of the viral diseases of roses.

Miri