It seems like the basis for your argument is that you have a...

It seems like the basis for your argument is that you have a data cap on your Internet connection, or that you are thinking of a home Internet connection as a system that exists solely for filling in govt or business forms. It sounds like you think about your Internet connection very differently to most people. For instance, I have an Internet connection because I like to watch videos and keep in contact with friends via the Internet. It is a bonus that I also get to order things, or fill in forms online as it is much easier for me than having to physically take an object to a post box or office.

Sure, you might get a reply paid envelope, but you then have to take the stupid thing somewhere and deal with it. I'm happy to pay an infinitesimal fraction of a cent to remove the hassle of not only filling in a form, but then actually taking it to a place to post it.

On the total replacement of paper: have you ever heard the saying "When the only tool you have is a hammer, every problem looks like a nail"? To put it another way, I think you have at some stage placed the Internet on a pedestal and are simply disappointed that it has not met your expectations by now.
"The complete replacement of paper" seems more like 90's media hype than anything that is actually achievable, even in the next 10 years. To say that the Internet has failed to replace paper is hyperbole as from where I'm sitting, it seems to be doing a great job at replacing paper, where it can.

My unsolicited advice is to simply wait longer or learn to code and start inventing solutions to the problems you see. The Internet is built on the things where people have done exactly this and the world is a much better place for it.

Sorry if I have missed the point of your argument, I'm having a hard time understanding exactly what the issue is.