resource_group=your_rg
namespace=your_namespace
topics=$(az servicebus topic list --resource-group $resource_group --namespace-name $namespace)
ids=""
for i in $(seq 0 $(echo "${topics}" | jq '. | length'))
do
ids="$ids $(echo "${topics}" | jq ".[$i].id")"
done
az servicebus topic delete --resource-group $resource_group --namespace-name $namespace --ids $ids