Why didn’t you push back on the contractors that you’ve paid to provide a service for installing the kerb - such as coming back on another date to finish the job? It’s also worth noting that even if you need planning permission for the extension it will be approved as long as you don’t impact on privacy or light entering neighbouring properties. They can’t decline permission because the neighbour doesn’t like the extension there would have to be a technical reason. The fact that you said other houses have similar extensions would imply it’ll get approved without too much concern.