C# Asp Net MVC is there a framework who can fill out a Form on an external Website automatically (Azure)

I searched in the last 3 days for some solution and this is my first question here so please be easy on me. I try to fill out a form on an external website with my ASP NET MVC Application. Sadly the Website doesnt support IE in the "normal" version anymore so using the normal Webbrowser doesn't work. I tested some Frameworks like Phantomjs, Selenium etc but they all use GDI+ so they can't use in Azure App Service. Is there another possiblity to solve this problem or do I need a Azure VM / need of some external service like browserless.io?

Thank you all in advance!