real quick check before the settings checks i will tell you to check...
do you have either or both your Samsung Account/Google Account on one,both, or either of the devices? if yes, did you use that account and device to help set up the other? if yes, remove the tablet from the account (if there), unsync the tablet and phone in the account (or "connected devices").
let me know either way so I can assist you further.
in the meantime, for a bandaid fix real quick... go to settings in the tablet, then accessibility, hearing enhancements, mute all sounds turn on so you won't hear the ringing and can still get all your notifications and such that turning on do not disturb would block.
