Call Status is always 'Establishing' but never turned to established - Calling bot for Microsoft Team- Application Hosted Media

I am really new to bot framework, I am currently working on a bot that is supposed to receive incoming (peer-to-peer) calls from Microsoft Teams using [Graph Calling SDK] and [Real time media library] and play an audio file (stored in a folder in my application) and get details of incoming audio media stream. My application is basically a .net framework 4.7.2 console application and i am trying to follow 'AVPFrontend' and 'HueBot Samples. Now the problem is when i don't involve any media configuration, bot answers the call and call is never disconnected. But when i include media platform settings, call status is never turned to 'Established' but it's always 'Establishing'

Following are my media platform settings:

builder.SetNotificationUrl(new Uri(ConfigurationManager.AppSettings["BotBaseURI"] + "api/calling"));
            builder.SetMediaPlatformSettings(new MediaPlatformSettings()
            {
                MediaPlatformInstanceSettings = new MediaPlatformInstanceSettings()
                {
                    CertificateThumbprint = "1c9bfea46besdfjsdk234234230e217b821666cf3f6",
                    InstanceInternalPort = 8500,
                    InstancePublicPort = 10119,
                    InstancePublicIPAddress = new IPAddress(0x0),
                    ServiceFqdn = "0.bot.conntoso.com",

                },

                ApplicationId = AppID,
            }
            );
            builder.SetServiceBaseUrl(PlaceCallEndpointUrl);

I am using ngrok to test and debug ngrok locally, following are my settings:

Expected behavior
The Call Status should turn to 'Established'

Additional context
From AVPFrontEnd sample, I have implemented PlatformCallController.cs (which addresses incoming call) and DemoController.cs (this should handle webhooks once call is accepted, according to my understanding). but code in DemoController.cs is never executed.
What am i missing, please help me to address this issue. Thanks!

Compare the AVPFrontend and HueBot samples with PlatformCallController.cs and DemoController.cs, then review the supplied MediaPlatformSettings and ngrok setup. Trace the incoming-call and webhook flow first, including where call status changes and where callbacks are logged. Done means the call reaches Established and DemoController.cs receives the expected webhook.