Trying to set boundaries is a very misleading approach and focuses your conversation on what you DON"T want. "You don't get to talk to me that way..."

It's not that you are wrong - it's that your approach did not achieve your goal and did not offer your mother clarity with respect to how you WANT her to talk to you.

Next time tell her what you need - and what kind of conversation is appropriate. It might also help to let her know that you are aware that she is coming from a good place AND that as parents you can assure her that you are taking all measures to take care of your son.