Enterprise sales

I'm currently trying out my hand on enterprise sales. Meaning I'm trying to sell my services to (at least) one large company.

The situation is this: There is an enterprise that has a need. The need is very clearly defined, meaning that they know exactly what it is that they need and how the solution is supposed to look. They do not know the technical details, but they don't need to, otherwise they wouldn't need an external supplier. The need is also unserved at the moment, and has been so for at least 15 years. They have a budget for their need, and since this is an important business and legal need, they spend that budget on fulfilling the need manually, ie. with paper and personnel. Essentially, they're stuck in the 20th century and want to upgrade to an internet-based service, both for modernity, for customer reach and for cost reasons. For the past 15 years, they didn't find a provider or a solution that could elevate their need into the internet.

I have a prototype for their need. This prototype clearly demonstrates how I would solve their business need and the necessary maths behind it. It's not simple, but straightforward.

I would like to present that prototype to the enterprise, showing them how easy it would be for them to get their need fulfilled and how reasonably priced.

But they don't want to see it. They say they're "not ready for this yet". Wow!

Ok, so I called their next-largest competitor which has the exact same need. Legal necessities and so on.
Or rather, I tried calling them, because I can't even reach anyone there.

Enterprise sales are frustrating.