I haven't used Cognitive
and C#, but you can find Azure Resource Management Package From here.

And you will find operations for Account.

Maybe you can search it by keywords above in Github, and find this piece of code.
//public static CognitiveServicesAccount CreateAndValidateAccountWithOnlyRequiredParameters(CognitiveServicesManagementClient cognitiveServicesMgmtClient, string rgName, string skuName, string accountType = Kind.Recommendations, string location = null)
//{
// // Create account with only required params
// var accountName = TestUtilities.GenerateName("csa");
// var parameters = new CognitiveServicesAccountCreateParameters
// {
// Sku = new Microsoft.Azure.Management.CognitiveServices.Models.Sku { Name = skuName },
// Kind = accountType,
// Location = location ?? DefaultLocation,
// Properties = new object(),
// };
// var account = cognitiveServicesMgmtClient.CognitiveServicesAccounts.Create(rgName, accountName, parameters);
// VerifyAccountProperties(account, false, accountType, skuName, location ?? DefaultLocation);
// return account;
//}