If it's excessive, then Google shouldn't have offered an unlimited data plan. They could have called it a 100 TB plan, but they chose to call it unlimited to make it sound better and then canceled it once people took them up on the offer. Regardless of whether that kind of action is legal, it's a shady business practice.

For that matter, there's nothing wrong with Google discontinuing the plan going forward, but they had plenty of options for making the transition more fair and building consumer trust without hurting their bottom line too much. For example, they could have converted his account to a 250TB account and tripled its price, at which point he wouldn't be in immediate danger of losing his files but would be pressured into gradually moving to a more cost effective solution.