Creating excel file and editing it using C# ASP

I have been working on a task for a long time and to no avail, I still cant solve it. I need to create an excel file in ASP .net and manually write the data. Much more like looping through the cells and do writing on specific cells as well as merging them. I cant use third party components and also, after the the excel file has been created and populated it should pop-up with the user.

If anyone can provide an example or at least provide an idea on how can this be possible, it will be a great help because it's been a frustrating month for me working on this.

Thanks in advance.