Good news. Your mower is covered by a 5 year warranty. Battery and charger have 3 year warranties. Give EGO customer service a call and they will help you out. Best to call early in the day to avoid hold times. They can be reached at 1-855-EGO-5656 (1-855-346-5656) from 8:30AM - 8:00PM EST (Monday - Friday) & 10:00AM - 6:00PM EST (Saturday & Sunday).
Just a quick troubleshooting step, have you double checked that the handle clamps are well inserted? Unclamp them, make sure the handle is fully extended and reclamp them in place.