What would you do?

Okay so me & my ex work together we broke up a couple months ago, this girl who has a boyfriend has been flirting with him and is acting like a b***h towards me. So is her twin sister who also works there. I’m not gonna lose my job over them and usually just ignore them, its work I’m gonna be civil but they want to be petty. What would you do? Just continue ignoring them & hope they grow up? 🙄 She lied and said I didn’t give her headset because she didn’t want to wait for me to finish taking the order (my manager saw I was taking an order but didn’t say anything) so I didn’t get a break that day. I was pissed. Like I don’t care if you don’t like me but its work, grow up. (I don’t work on days my ex does nor do i talk to him, he isn’t the problem she is) I’m just gonna continue ignoring and avoiding them but yeah. Its just annoying.. *sigh*