I've briefly encountered similar issues in the past
Most of the overruns ceasing abruptly when I asked one simple question.
"Are you comfortable with the phrase fundamental breach of contract?"
Suddenly, the cost overruns ended, date slippage ceased and progress ensued, as under our laws, a fundamental breach of contract is not only fully recoverable, but damages can be awarded. The contracting company then has to figure out, free product and services *and* pay damages or absorb their illegally massive underbid, as such is simply fraud to acquire a contract. Plus, awarded damages, losses and oh yeah, getting blacklisted as a vendor in perpetuity.