nonstop call witing beep

I’ m using an iphone X. My software version is 15.2. After I getting updated to version 15, there is nonstop beep when I’m receiving 2nd call and it never stop (nonstop call waiting beep). This is really irritating and I can’t continue my first call (existing call) with this nonstop beep of second call. I tried to stop volume up and down keys to stop this beep but didn’t work. This is really a annoying please help.