The UriBase might need to be changed form the old cognitive services uri to the new bing uri. I was just working with some sample code that had to be updated as follows:
OLD:
const string UriBase = "https://api.cognitive.microsoft.com/bing/v7.0/images/search";
NEW:
const string UriBase = "https://api.bing.microsoft.com/v7.0/images/search";