There is context to that promise of "unlimited". The government bought one cheap consumer-oriented cellular internet plan for their mission critical emergency communications. There is a bit of mismatch on the intended purpose of the offer. I'm sure you'll even find a disclaimer of liability and disclaimer of suitability/warranty in the contract. The government f'ed up, no way around it.

And I'd wager heavily that the government employees/contractors had ample budget to read the contract.