Azure Notification Hub .Net SDK Methods are not working

I started using Azure Notification Hub to send PUSH to Android and iOS devices. To send PUSH i am using .net SDK. I created a REST API to allow device to register on Azure Notificaion Hub and internally this REST API is calling .net SDK methods. But when I call these .net SDK methods inside of REST API its don't return any response and if I call same method through some windows/Console .ent application all are working fine. The methods names are mention below.

_NotificationHubClient.GetRegistrationAsync<RegistrationDescription>(registrationId);

_NotificationHubClient.SendTemplateNotificationAsync(param); ;

Installation ins = _NotificationHubClient.GetInstallation(registrationId);

All get and send methods are having same problem. Only  _NotificationHubClient.CreateOrUpdateInstallation(newInstallation) is working fine.