Your brother surely did a wrong act. He had no right to emphasise on showing him the text. Siblings sometimes banter and tease; that's another thing but taking it as their right to invade your privacy is totally wrong.
I also value my and other people's privacy a lot. With children the matter is different but with adult trust is the only thing that should be built to figure out issues in their lives.
At the time, he felt because he was older than I was, that that gave him the right to phone.. I was happy I refused and stood my ground.
👍