Sticky black coating and curled new leaves on my chilli with ants around

The soft clustered insects on new shoots, the sticky feel and the black sooty coating are aphids. They suck sap, secrete a sugary honeydew that ants collect, and the sooty mould grows on the honeydew. Aphids also spread viruses, so control matters. Often a strong jet of water knocks them off, and natural enemies like ladybird beetles control light infestations, so avoid harsh sprays that kill those friends. For heavier loads spray neem oil or insecticidal soap first, and if needed a recommended insecticide such as flonicamid or imidacloprid, rotating modes of action. Control the ants too since they protect the aphids from predators. The sooty mould itself washes off once the aphids are gone. As chilli is eaten fresh, follow the label dose and pre-harvest interval, and confirm with your KVK if you are unsure.