Help me be petty

Okay so my partner cheated on me with his ex at the start of my pregnancy, I’ve chose to stay blah blah blah ANYWAY I have found her number and want to message/call her but just to find out if it’s actuallly her, or would love to see if she still talks to my partner (don’t think she does) BUT I don’t want to let on it’s me or have my partner know (psycho, I know) any suggestions? Prank call? Text her off my number and say hey it’s my new number? I’m sure I’m not the only one to want to do this?