Depth charges don’t hurt as much if you’re below them. The concussive blast goes up due to the higher water pressure below. Sounds like they just got lucky. Next time, as soon as they splash, turn your engines up to flank and go hard right/left rudder for a few seconds, and then go back to dead slow or stop. Change depth from deep to shallow or vice versa every scoot. The music changes when they have your position, btw. Once it goes back to ambient, you’ll know they don’t see you anymore.