If it still persists then contact your carrier
What's the error/alert that it's giving you when you try to call?
I think this is more of a carrier issue(Thank you @Tallman and @Echo1), so try following their advice and checking the sim card status and mobile carrier status as well.
Placing call results in other side unable to hear anything. Getting calls with freshly reset still unable to answer regardless of using Accessibility Options or tapping accept as is displayed so briefly before disappearing.
Prior to this latest update was fine....