Using file upload widget and check if file exists then Comfirmation popup is appearing multiple time

I am working on file upload widget. 
Uploaded files are stored in Repository.

Written a service to check if uploaded file exists in repository. Calling that on mashup. It returns either true or false.

If file exists confirmation popup appears.

Issue is My confirmation popup appears more than two times. Service is triggering multiple times.

I have binded the validation event for file upload to my file exists service.

Please provide a solution.