If you bought from US, then US has the responsibility to notify and rebook. That they hadn't notified you for a June flight change isn't surprising; some carriers/systems wait until 30 days before first flight.

Intransigence in rebooking is a surprise - they usually want to keep your money. If flight times or day-of-week service reductions force an overnight sometimes it's better to take a refund and do-over on another carrier (after researching options and prices), but CLT overnight at your expense and CLT-SFO the next day should have been offered.