Getting The underlying connection was closed

I developed my own dashboard and displying powerbi dashboad and reports with dataset refresh feature. it was working fine for the last one year but for the last few days suddenly it stop working and showing "The underlying connection was closed: An unexpected error occurred on a send".

Just for more clarity i was following below steps to refresh the dataset as well as display reports

Refresh Data set:

1. Generate the Access token : getting access token 

2. call API https://api.powerbi.com/v1.0/myorg/groups/{0}/datasets/{1}/refreshes   passing groupid, datasetid, token etc

Here i am getting error: "The underlying connection was closed: An unexpected error occurred on a send"

Same error while try to get information for reports.